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Hormone Regulation of
Elasmobranch Physiology
Chris Bedore and Shannon Long
What We’ll Be Covering
• Digestion and Energy
Metabolism
• Growth
• Stress
• Osmoregulation
• Physiological Color
Change
• Reproduction
• Reproduction
• Reproduction
• Research methods
Things to Remember
DIGESTION AND ENERGY
METABOLISM
The Players
• Secretin—stimulates secretion of bicarbonate-rich
pancreatic juices
• Cholescystokinin (CCK)—regulates supply of bile
and pancreatic enzymes
• Somatostatin (SS)—suppress production of gastric
acid, inhibit rectal gland secretion, inhibitory regulation
of GH from hypothalamus
• Neuropeptide Y (NPY)—promote digestion by
increasing blood flow, inhibits gastric acid secretion,
pancreatic enzyme release, and gallbladder
contraction, inhibit rectal gland secretion
• Bombesin/Gastrin-releasing peptide (GRP)—
promote digestion by increasing blood flow, effecting
acid/enzyme secretion/gut motility, inhibit rectal gland
secretion
• Vasoactive intestinal polypeptide (VIP)—suppress
digestion by reducing blood flow, effecting acid/enzyme
secretion/gut motility, stimulates salt excretion by
vasodilating the rectal gland and increasing cellular
cAMP enzyme, used to regulate water and ion balance
• Tachykinins—promote digestion by increasing blood
flow, effecting acid/enzyme secretion/gut motility
• Insulin—storage/conversion/uptake of energy substrate,
pancreas, regulated by nutrient levels, reduction in
circulating amino acid levels, no effect on ketones
• Glucagon—antagonistic to insulin
• Thyroid—alter levels of enzymes in amino acid/lipid
metabolism
DIGESTION AND ENERGY
METABOLISM
GROWTH
The Players
• Growth hormone (GH)—pituitary gland,
regulated by GHRH, promotes somatic and
skeletal growth
• Growth hormone-releasing hormone
(GHRH)—regulates GH, stimulatory from
hypothalmus
• Insulin-like growth factors (IGF-I)—promotes
growth of vertebral column
STRESS
The Players
• Chromaffin tissue—masses of neurosecretary cells
on kidney, cells secrete epinephrine and
norepinephrine, response to acute stress
• Catecholamines—epinephrine and norepinephrine,
promote mobilization, of energy reserves, increase
blood pressure, blood flow to gut reduced, increase
oxygen uptake in gills
• Hypthalamo-Pituitary-Interrenal axis (HPI axis)—
mid-axis lengthwise down body, helps to regulate ions
• Corticosteroids—interrenal body, regulated by ACTH,
promote nutrient movement through body, inhibit
growth and energy storage, aid in retention of sodium
• Adrenocorticotropic hormone (ACTH)—regulates
corticosteroids, stimulated by CRF, induces
hyperglycemia
• Corticotrophin-releasing factor (CRF)—
hypothalamic compound, stimulates ACTH, regulate
interrenal production of 1α-OHB
• 1α-Hydroxycorticosterone (1α-OHB)—corticosteroid
produced only in elasmobranchs, stimulate retention of
sodium and chloride
OSMOREGULATION
The Players
• Renin-angiotensin system (RAS)—used to regulate
water and ion balance, series of biochemical steps
1. convert hepatic glycoprotein angiotensinogen to
ANG I
2. cleavage to ANG I by ACE makes ANG II
• Angiotensin I (ANG I)—inactive form
• Renin—enzyme used to convert to ANG I, secreted by
juxtanglomerular cells of kidney
• Angiotensin converting enzyme (ACE)—promotes
cleavage in ANG I to make ANG II
• Angiotensin II (ANG II)—biologically active, receptors
in interrenal gland/gill/rectal gland/intestine, modulate
HPI axis, stimulates 1α-OHB secretion, promotes
sodium retention, influence electrolyte balance by
reducing GFR and UFR, inhibits salt release from
rectal gland, increase drinking rate
• C-type natriuretic peptide (CNP)—used to regulate
water and ion balance, stimulates production of VIP
and rise in salt secretion, expressed in heart and
brain, responds to increased cardiac pressure, directly
affects rectal gland epithelial cells, binds to NPR-B to
increase cGMP and PKC, dilates rectal gland to cause
increase in salt release
• Natriuretic peptide type-B (NPR-B)—in rectal gland
epithelium
• Cyclic granosine monophosphate (cGMP)
• Protein kinase C (PKC)
• Arginine vasotocin (AVT)—regulates
osmoregulation, reduces diuresis
PHYSIOLOGICAL COLOR
CHANGE
The Players
• Melanocyte—type of chromatophore, contains
melanosome which has brown-black melanin
• α-Melanocyte-stimulating hormone (αMSH)—regulates physiological color change,
produced in neurointermediate lobe of pituitary,
when removed- sharks lighten in
color,
when expressed- sharks darken, controlled by
neural signals to hypothalamus
• Melatonin—induces skin pallor
• Prolactin (PRL)—in par distalis of pituitary, in
freshwater ray, regulates physiological color
change
What Goes On Inside
Reproductive Endocrinology- Overview
diverse breeding strategies in elasmos
therefore, probably diverse regulatory mechanisms
this area is largely unknown and mostly hypothetical
information is from hormone concentration at a
specific time in mating season and deduced
from other vert spp.
well studied in only a few species
(ex: D. sabina, S. tiburo)
Reproductive Endocrinology- Overview
Brain-Pituitary-Gonad (BPG) axis:
primary endocrine regulation, initiated by env. stimuli
Reproductive Endocrinology- Overview
gonadal steroids:
regulate gametogenesis, modulate reproductive
behavior, modulate development and function of
2⁰ sex characteristics
influence production of GnRH and GTH (neg. feedback)
steroid binding sites in hypothalamus
potential to alter production of relaxin, calcitonin,
thyroid
most cycle throughout mating season
Reproductive Endocrinology- Anatomy
Reproductive Endocrinology- Anatomy
GnRH
Gonadotropin-releasing hormone:
many forms (7?), therefore many functions
dfGnRH, sGnRH, cIIGnRH, mGnRH
GnRH and GnRH-BPs present in systemic circulation
direct action on gonads?
different forms present in different parts of the brain
Hypothalamus/Forebrain: regulate GTH
GnRH
Pituitary/Forebrain: regulate pituitary/gonads, convey
env. info to initiate BPG
GnRH
Terminal nerve: regulate repro. processes?!
GnRH
Midbrain/Hindbrain: regulate sensory sensitivity during
reproduction (ie-e-reception)? clasper movement
GTH
gonadotropin hormone
pituitary gland
partially regulate steroidogenesis, gametogenesis
(systemic GnRH)
response to GTH may depend on env. stimuli (H2O temp,
photoperiod) and reproductive stage
2 types found so far in elasmos
similar structure to FSH, LH in tetrapods?
*future research*
Female Steroids-Gonadal
3 major gonadal steroids:
17β-estradiol (estrogen)- E2
Progesterone- P4
Testosterone- T
Female Steroids-Gonadal
Female Steroids-Gonadal
E2
2 peaks
1. pre-ovuation/follicle development
stimulate vitellogenesis
regulate development of oviducal gland
2. late gestation (Squalus acanthias)
regulate vitellogenesis
regulate secretion of histotroph (Dasyatis sabina)
Female Steroids-Gonadal
P4
suppress vitellogenesis (opposes E2)
viviparous: peaks close to ovulation
↓ late gestation-permits next follicles to develop
(S. acanthias)
oviparous: regulate timing of oviposition (↑=oviposit)
Female Steroids-Gonadal
T and DHT (androgens)
↑ during follicle development
precursor to E2 synthesis
modulate copulatory behavior
sperm storage (T)
regulate oviposition?
*future research- distribution of receptors*
Female Steroids-Other
Female Steroids-Other
Relaxin (Rlx)
found in ovary of several species
implant and removal experiments↑ cervical area- prep for parturition
probably aids pupping and oviposition
maintains uterus during gestation (↓ contractions)
Sphyrna tiburo- participates in ova release?
Female Steroids-Other
Thyroid (T3 and T4)
interacts with BPG axis, role unknown
↑ during ovulation and gestation (D. sabina)
associated with > metabolic costs at this time?
S. tiburo highest levels- placental formation
Female Steroids-Other
Thyroid (T3 and T4)
embryo- passed to young through yolk (McComb et al. 2005)
regulate rate of development
> concentration found in yolk from populations with:
larger birth size
faster rate of development
greater size at maturity
higher maternal investment
Female Steroids-Other
Calcitonin (CT)
produced in ultimobranchial gland
muscles between pharynx and pericardial cavity
↑ in response to E2 binding on gland
maternal gill: ir-cells
regulate Ca2+ homeostasis during gestation?
mechanism/role unclear
Female Steroids-Other
Calcitonin (CT)
S. tiburo: peaks during yolk dependent stage
asstd w/digestion of yolk? ir-cells in duodenum &
pancreas of early embyros
Female Steroids-Other
Calcitonin (CT)
D. sabina: peaks during histotroph production
no ir-cells in embryo, therefore not involved in
embryo nutrition
Male Steroids-Gonadal
mostly produced in Sertoli cells (in testes)
Leydig cells: supplements gonad steroids for regulating
stages of spermatogenesis
(epididymis and ductus deferens)
trends differ among spp, but all regulate aspects of repro.
Male Steroids-Gonadal
4 major gonadal steroids:
Testosterone (T)
Dihydrotestosterone (DHT)
Progesterone (P4)
17β-estradiol (E2)
Male Steroids-Gonadal
Male Steroids-Gonadal
T and DHT (androgens)
↑ middle to late spermatogenesis
= peak GSI (high # spermatocytes in testes)
influence development of spermatogonia and repro. ducts
routes of hormone transfer between testes and urogenital
system:
systemic circulation, binding sites in spermatozoa,
enzymes in semen
Male Steroids-Gonadal
T and DHT (androgens)
claspers/cartilage: calcification due to androgens?
indirect evidence, but no direct evidence
coincides with androgen peak
enlarged S. tiburo cephalofoil during male
pubertal development
but- implant/removal experiments showed no
relationship
mediated through GH and IGF-1 (after E2 peak)?
*future studies*
Male Steroids-Gonadal
T and DHT (androgens)
Male Steroids-Gonadal
E2
unsure of role in males- some spp show cycling patterns (D.
sabina), irregular variations in others (S. tiburo)
D. sabina:
receptors in epididymis and seminal vesicles
maintain repro. tract function?
peak early-middle spermatogenesis
regulate early spermatogenesis?
*future studies*
Male Steroids-Gonadal
P4
cycle mirrors androgens (S. tiburo)
substrate for androgen synthesis?
but- pubertal S. tiburo & D. .sabina:
peak precedes androgen peak
regulate spermiogenesis and/or spermiation?
Male Steroids-Other
Relaxin (Rlx)
produced by gonads
other verts: regulate male fertility
S. tiburo:
↑ during late spermatogenesis and copulatory period
[relaxinsemen]=1000x [relaxinblood]
facilitate insemination through contractability of
repro tract of postmated female?
Male Steroids-Other
Thyroid (T3 and T4)
seasonal cycling
peak spring and fall
aid in ↑ metabolic needs during migration?
*future studies*
Gonadal Steroid & Development
*effect of steroid hormones on development needs more
research!*
E2, P4, T transferred from female to yolk
E2, T probably utilized during development
BPG axis activated during maturation
steroidogenesis
stage specific increases of hormones (S. tiburo), but
roles unclear
Hormones and Behavior
androgens peak in males during copulatory period in some
species (ex: D. sabina)
may influence certain behaviors- aggression
ex: protracted mating period/aggression D. sabina
may also affect sensory sensitivities
ex: electroreception in D. sabina
Dasyatis sabina
Tricas et al., 2000
spermatogenesis:
production and development of spermatozoa
spermiogenesis: last stage; produces mature spermatozoa
spermiation: release of spermatozoa from Sertoli cells
spermatogonium → spermatocytes → spermatids →
spermatozoa
Dasyatis sabina
Tricas et al., 2000
male steroid hormones:
4 phases:
1. androgen suppression
2. PAI, peak E2, P4
3. androgen decrease
4. SAI
Dasyatis sabina
phase 1:
androgen suppression
between mating seasons
Dasyatis sabina
phase 2:
primary androgen
increase
E2, P4 increases
maximum spermatocyte
development (max GSI)
Dasyatis sabina
phase 3:
androgen decrease
following maximum testis
growth and
spermatocyte
development
E2 and P4 also decrease
Dasyatis sabina
phase 4:
secondary androgen
increase
peak sperm maturation
copulatory period
Dasyatis sabina
Female hormones
androgens
small, brief peaks winter,
spring
aggression during mating
period?
Dasyatis sabina
Female hormones
E2:
1st peak- maturation of
oocytes (March); synthesis
and uptake of vitellogenin
2nd peak- late
development, parturition
transition yolk to
histotroph? *future
studies*
Dasyatis sabina
Female hormones
P4:
1st peak: near ovulation
2nd peak: parturition
Dasyatis sabina
androgens, behavior, and protracted mating period:
courtship behaviors- males follow females nose to vent
chase, bite fins
females- enhance mate choice by fleeing
Reproductive Endocrinology- Methods
Immunocytochemistry,
Immunohistochemistry
(ICC, IHC):
ir-staining of desired
hormone
ex: GnRH neurons in
hypothalamus or
terminal nerve
Reproductive Endocrinology- Methods
ICC, IHC:
-collect tissue samples
Reproductive Endocrinology- Methods
ICC, IHC:
- section tissue
Reproductive Endocrinology- Methods
ICC, IHC:
- apply primary antibody, apply secondary antibody
with enzyme, provide substrate, then counter-stain
Reproductive Endocrinology- Methods
Control
Electro-Stimulated
Female
Male
P. marinus GnRH neurons (top-female, bottom-male) before (left column) and after
(right column) electro-stimulation
Reproductive Endocrinology- Methods
Radioimmunoassay (RIA)
Reproductive Endocrinology- Methods
Radioimmunoassay (RIA)
uses radiolabeled (ex: 3H) antibody for competitive
binding to hormone
calculate % bound radiolabel to determine hormone
concentration in a sample
Reproductive Endocrinology- Methods
hormone implants
ex: Sisneros and Tricas, 2000
surgically implant hormone tablet/capsule into body
wait for it to take effect (usually a # of days)
check for changes (RIA, behavior, electrophysiology)
Reproductive Endocrinology- Methods
hormone implants
Reproductive Endocrinology- Methods
organ removal (ie pituitary, hypothalamus)
similar to hormone implant, but remove organ
wait for it to take effect
check for changes (RIA, behavioral,
electrophysiology)
Conclusion/Future Research
hormone regulatory mechanisms seem to be similar
to other vertebrates
many vertebrate hormones first appeared in
elasmobranchs
MUCH research is needed to determine roles of many
hormones. There is less information on elasmo
hormones than any other vertebrate group, despite
evolutionary role. We need to catch up!
Literature Cited
Chung-Davidson, Y.-W., M.B. Bryan, J. Teeter, C.N. Bedore, and W. Li. 2007. Neuroendocrine
and behavioral responses to weak electric fields in adult sea lampreys
(Petromyzon marinus). Hormones and Behavior. (In Review)
Gelsleichter, J. 2004. Hormonal Regulation of Elasmobranch Physiology. Pp. 287-324 in Biology
of Sharks and Their Relatives (J.C. Carrier, J.A. Musick, and M.R. Heithaus, eds).
CRC Press, Boca Raton.
Kajiura, S.M., J.P. Tyminski, J.B. Forni, and A.P. Summers. 2005. The sexually dimorphic
cephalofoil of bonnethead sharks, Sphyrna tiburo. Biol. Bulletin 209: 1-5
Sisneros, J.A. and T.C. Tricas. 2000. Androgen-induced changes in the response dynamics of
ampullary electrosensory primary afferent neurons. J. Neurosci. 20(22): 8586-8595.
Tricas, T.C., K.P. Maruska, and L.E.L. Rasmussen. Annual cycles of steroid hormone
production, gonad development, and reproductive behavior in the Atlantic stingray.
Gen. Comp. Endocrin. 118: 209-225.
Trivett, M.K., T.I. Walker, D.L. Macmillan, J.G. Clement, T.J. Martin, and J.A. Danks. 2002.
Parathyroid hormone-related protein (PTHrP) production sites in elasmobranchs.
J. Anat. 201: 41-52.