Identification and characterization of arginine vasopressin-like substances in the rat testis

Vasopressin regulates hypothalamic GnRH synthesis: Histomorphological evidence in hypothalamus and biological effects in GT1-7 cells

AIMS

To investigate the direct histomorphological clues and observe the biological effects of VP acting on gonadotropin-releasing hormone (GnRH) secretion.

MAIN METHODS

Immunofluorescence was conducted to investigate the expressions of GnRH and VP in experimental left varicocele (ELV) rats and ELV repair rats. The colocalization of GnRH and VP was observed by electron microscopy immunohistochemistry. The protein-protein interaction between GnRH and VP was tested by co-immunoprecipitation (co-IP) and the proximity ligation assay (PLA). The effects of intracellular and extracellular VP on GnRH and relative transcription factors (Oct-1, Otx2, Pbx1b and DREAM) were respectively evaluated in VP overexpressed and VP treated GT1-7 cells.

KEY FINDINGS

Both hypothalamic GnRH and VP decreased in ELV rats and recovered by ELV repair. The overlapped immunolocalizations of GnRH and VP mainly distributed in the lateral part of the arcuate nucleus (ArcL) and median eminence (ME) with a Manders' overlap coefficient of 0.743 ± 0.117. Immunoreactive substances of GnRH and VP existed in the same and adjacent terminals. VP overexpression did not cause any significant effects on the expressions of GnRH and Oct-1, as well as GnRH promoter activity. While 50-200 pg/ml VP treatments increased GnRH mRNA levels in a dose- and time-dependent manner in GT1-7 cells. Additionally, 200 pg/ml VP triggered a marked promotion of expressions of GnRH, Oct-1, Oxt2 Pbx1b and DREAM, as well as GnRH promoter activity (P < 0.05).

SIGNIFICANCE

The results reveal the colocalization and interaction of VP and GnRH, which will be conducive to explain the effects and mechanisms of VP acting on reproduction.

In situ localization of vasotocin receptor gene transcripts in the brain-pituitary-gonadal axis of the catfish Heteropneustes fossilis: a morpho-functional study

In the catfish Heteropneustes fossilis, three vasotocin (VT) receptor subtype genes, v1a1, v1a2, and v2a, were cloned and characterized previously. In the present study, using RNA probes, we localized the distribution of the gene transcripts in the brain-pituitary-gonadal (BPG) axis. The V1a-type receptor, v1a1 and v1a2, genes showed similar and overlapping distribution in the brain. The gene paralogs are distributed in the radial glial cells (RGCs) of the telencephalic ventricle and around the third ventricle in the hypothalamus and thalamus, olfactory tract, nucleus preopticus, nucleus lateralis tuberis, nucleus recessus lateralis and posterioris, nucleus saccus vasculosi, thalamic nuclei, habenular nucleus, habenular commissure, basal part of pineal stalk, accessory pretectal nucleus, optic tectum, corpus and valvula of the cerebellum, and facial and vagal lobes. The V2a receptor gene (v2a) has restricted distribution and is largely confined to the anterior subependymal region of the telencephalon. The localization pattern shows that the V1a-type receptors are distributed in major sensorimotor processing centers and the neuroendocrine/reproductive centers of the brain. In the pituitary, the receptor genes were localized differentially in the three divisions with the V1a-type receptor genes strongly expressed in the rostral pars distalis compared to the v2a paralog. In the ovary, the V1a-type receptor genes were localized in the follicular layer while v2a was localized in the oocyte membrane. In the testis, v1a2 and v2a are densely distributed in the interstitial tissue and seminiferous epithelium but the v1a1 is lowly expressed. The results suggest that the VT receptor genes have an extensive but differential distribution in the BPG axis. Future experimental studies are required to correlate the cellular localizations with specific functions of VT in the BPG axis.

Motile Sperm Output by Male Cheetahs (Acinonyx jubatus) Managed Ex Situ Is Influenced by Public Exposure and Number of Care-Givers

The collective cheetah (Acinonyx jubatus) population in zoological institutions has never been self-sustaining because of challenges in natural reproduction. A retrospective analysis of North American zoo-breeding records has revealed that >90% of litters produced since 2003 occurred in facilities ‘off-display’ from the public. We examined seminal, endocrine, and behavioral traits of 29 adult male cheetahs that were: 1) managed in public exhibit or off-display facilities; 2) maintained by different numbers of cheetah-specific care-givers; and 3) living adjacent to varying numbers of adult conspecifics. Cheetahs housed off-display produced more total motile sperm/ejaculate (P = 0.04) than on-exhibit males. This finding was mirrored in our laboratory’s historical records where two-fold more total motile sperm (P < 0.01) were measured in ejaculates from individuals with no public exposure (n = 43) compared to on-exhibit (n = 116) counterparts. Males at institutions with ≤3 care-givers also produced more total motile sperm/ejaculate (P < 0.03) and spent more time behaviorally active (P < 0.01) than at facilities using >3 care-givers. Exposure to high numbers of conspecifics within the same institution did not impact (P > 0.05) seminal traits, and presence of the public, care-giver number, or animals/facility had no influence (P > 0.05) on androgen or glucocorticoid excretion or other behavioral metrics. Findings indicate that male cheetahs are sensitive to general public exposure and too many care-givers, resulting in compromised motile sperm output/ejaculate with mechanism of action unrelated to altered androgen or glucocorticoid excretion.

Arginine vasopressin inhibits adipogenesis in human adipose-derived stem cells

Intracellular Ca(2+) signaling is important for stem cell differentiation and there is evidence it may coordinate the process. Arginine vasopressin (AVP) is a neuropeptide hormone secreted mostly from the posterior pituitary gland and increases Ca(2+) signals mainly via V1 receptors. However, the role of AVP in adipogenesis of human adipose-derived stem cells (hASCs) is unknown. In this study, we identified the V1a receptor gene in hASCs and demonstrated that AVP stimulation increased intracellular Ca(2+) concentration during adipogenesis. This effect was mediated via V1a receptors, Gq-proteins and the PLC-IP3 pathway. These Ca(2+) signals were due to endoplasmic reticulum release and influx from the extracellular space. Furthermore, AVP supplementation to the adipogenic medium decreased the number of adipocytes and adipocyte marker genes during differentiation. The effect of AVP on adipocyte formation was reversed by the V1a receptor blocker V2255. These findings suggested that AVP may function to inhibit adipocyte differentiation.

Vasopressin effectively suppresses male fertility

Arginine vasopressin (VP) is neurohypophysial hormone has been implicated in stimulating contractile activity of the male reproductive tract in the testis. Higher levels of VP decrease sperm count and motility. However, very little is known about the involvement of VP in controlling mammalian reproductive process. The goal of this study was to confirm that effect of VP receptor (AVPR2) on sperm function in capacitation condition. Deamino [Cys 1, D-ArgS] vasopressin (dDAVP), an AVPR2 agonist that operates only on AVPR2, was used. Also, Mouse spermatozoa were incubated with various concentrations of dDAVP (10(-11)-10(-5) M) and sperm motility, capacitation status, Protein Kinase A activity (PKA), tyrosine phosphorylation, fertilization, and embryo development were assessed using computer-assisted sperm analysis, Combined Hoechst 33258/chlortetracycline fluorescence, Western blotting, and in vitro fertilization, respectively. AVPR2 was placed on the acrosome region and mid-piece in cauda epididymal spermatozoa, but the caput epididymal spermatozoa was mid-piece only. The high dDAVP treatment (10(-8) and 10(-5) M) significantly decreased sperm motility, intracellular pH and PKA substrates (approximately 55 and 22 kDa) and increased Ca(2+) concentration. The highest concentration treatment significantly decreased PKA substrate (approximately 23 kDa) and tyrosine phosphorylation (approximately 30 kDa). VP detrimentally affected capacitation, acrosome reaction, and embryo development. Treatment with the lowest concentration (10(-11) M) was not significantly different. Our data have shown that VP stimulates ion transport across sperm membrane through interactions with AVPR2. VP has a detrimental effect in sperm function, fertilization, and embryonic development, suggesting its critical role in the acquisition of fertilizing ability of mouse spermatozoa. These research findings will enable further study to determine molecular mechanism associated with fertility in capacitation and fertilization. It is also an important pivotal precondition to the progress of diagnostic test to identify infertility and to apply male contraception.

The role of arginine vasopressin in diabetes-associated increase in glucagon secretion

The purpose of this study was to investigate the role of arginine vasopressin (AVP) on glucagon secretion in both normal and diabetic rats. Diabetes was induced by intravenous administration of 50 mg/kg streptozotocin, 14 days before pancreatic perfusion. Diabetic rats were maintained on insulin replacement therapy until approximately 48 h before the perfusion experiments. Both glucagon and AVP were determined in the effluent of the perfused pancreas using RIA. Both normal and diabetic rats had similar basal glucagon secretion. AVP (3-30 pM) increased glucagon secretion from both normal and diabetic rats in a concentration-dependent manner. However, diabetic subjects were more sensitive to AVP administration than normal subjects with regard to glucagon secretion. By comparison of the areas under the curves, AVP-induced glucagon secretion in diabetic rats was approximately 2-fold that of the normal rats. In addition, immunoreactive AVP was detected in the effluent of the perfused pancreas, and diabetic rats had 70% higher AVP concentrations in the pancreatic effluent than normal rats. We conclude that AVP is secreted from the pancreas and diabetic rats can secrete more AVP from the pancreas than normal rats. Consequently, AVP may have a greater impact on glucagon secretion in diabetic subjects than normal ones. AVP might play an important role in the hypersecretion of glucagon in diabetic subjects.

Oxytocin and vasopressin expression in the ovine testis and epididymis: changes with the onset of spermatogenesis

Contractions of seminiferous tubules and epididymal duct walls promote spermiation and sperm transfer, and they are thought to be stimulated by the related peptides oxytocin and vasopressin. This study tested the hypothesis that if oxytocin and/or vasopressin play a physiological role in sperm shedding and transport, then local or circulating concentrations of these peptides would increase during puberty. Testes, epididymides, and trunk blood of sheep at stages during the first spermatogenic wave were collected, and radioimmunoassay measured significant increases in testicular and epididymal oxytocin during spermatogenesis. No changes were measured in circulating oxytocin or in local or circulating vasopressin. Localization and synthesis was investigated by immunohistochemistry and Western blot analysis employing antibodies recognizing epitopes of either oxytocin, oxytocin-associated neurophysin, vasopressin, or vasopressin-associated neurophysin. Marked expression of both oxytocin and its associated neurophysin in testicular Leydig and epididymal principal cells was seen, and weak neurophysin immunoreactivity was also identified in Sertoli cells. The intercellular distribution of oxytocin varied between regions of the epididymis, suggesting several roles for oxytocin. Vasopressin synthesis was not apparent in either tissue. These results confirm the presence and development of paracrine oxytocinergic systems in the ram testis and epididymis of ram during puberty while questioning the physiological importance of vasopressin.

Characterization of receptors mediating AVP- and OT-induced glucagon release from the rat pancreas

We characterized the receptors that mediate arginine vasopressin (AVP)- and oxytocin (OT)-induced glucagon release by use of a number of antagonists in the perfused rat pancreas and the fluorescence imaging of the receptors. AVP and OT (3 pM-3 nM) increased glucagon release in a concentration-dependent manner. The antagonist with potent V(1b) receptor-blocking activity, CL-4-84 (10 nM), abolished AVP (30 pM)-induced glucagon release but did not alter OT (30 pM)-induced glucagon release. d(CH(2))(5)[Tyr(Me)(2)]AVP (10 nM), a V(1a) receptor antagonist, and L-366,948 (10 nM), a highly specific OT-receptor antagonist, failed to inhibit AVP-induced glucagon release. In contrast, L-366,948 (10 nM) abolished OT (30 pM)-induced glucagon release but did not change the effect of AVP. Fluorescent microscopy of rat pancreatic sections showed that fluorescence-labeled AVP and OT bound to their receptors in the islets of Langerhans and that the bindings were inhibited by 1 microM of Cl-4-84 and L-366,948, respectively. Because AVP and OT at physiological concentrations (3-30 pM) increased glucagon release, we conclude that AVP and OT increase glucagon release under the physiological condition through the activation of V(1b) and OT receptors, respectively.

Opposite changes in the content of oxytocin- and vasopressin-like immunoreactive peptides in the rat thymus during aging

The content of oxytocin- and vasopressin-like immunoreactive (IR) peptides was measured in the thymic extract of 2, 5, 10, 15 and 20 month-old rats by radioimmunoassay before or after fractionation by high-pressure liquid chromatography. In both cases the content of the oxytocin-like IR peptide, which behaved like authentic oxytocin in the chromatography column, increased during aging. Compared to 2 month-old rats a significant 30% increase was observed in 5 month-old rats, whereas the maximal increase (200%) was found in 20 month-old rats. In contrast, the content of the vasopressin-like IR peptide, which behaved like authentic arg8-vasopressin in the chromatography column, decreased during aging. The decrease (30%) was evident in 5 month-old rats, and was maximal (80%) in 15 month-old rats. The present results suggest that the mechanisms regulating the content of oxytocin- and vasopressin-like IR peptides in the rat thymus undergo differential changes during aging. These processes might be linked to thymic involution.

Identification of vasopressin mRNA in rat aorta

We have reported previously that several blood vessels of the rat and cow contain immunoreactive vasopressin and further suggested that this peptide might be produced locally. To provide additional support for this hypothesis, we conducted the present study to determine whether mRNA for arginine vasopressin is also present in blood vessels. Ribonuclease protection analysis of total RNA isolated from rat hypothalamus and aorta revealed the presence of arginine vasopressin message in both tissues but not in RNA isolated from liver, a tissue devoid of vasopressin. Subsequent comparison of the autoradiographic intensities of the signals in these two tissues indicated that vasopressin message was 100- to 1000-fold lower in aorta. Additional studies showed that RNA isolated from endothelium-denuded vessels contained levels of arginine vasopressin message similar to those in intact vessels, indicating that endothelium was not a major source of this message. These data were substantiated by further studies using a vasopressin radioimmunoassay, which showed that vasopressin peptide levels in intact and endothelium-denuded vessels did not differ. Thus, the present study showed that rat aorta contains arginine vasopressin mRNA as well as the vasopressin peptide and that both the message and the peptide are contained in nonendothelial structures. However, the data do not rule out endothelium as a possible source of vasopressin. These studies add further support to the hypothesis that blood vessels are capable of producing vasopressin.

The effect of [Arg8]vasopressin on electrogenic chloride secretion in cultured rat epididymal epithelia

Primary cultured rat efferent ductal epithelia and cauda epididymal epithelial were mounted in Ussing chambers to study the effect of arginine vasopressin (AVP) on chloride secretion in the male excurrent duct. The regional differences in the signal transduction pathways involved were also investigated. In both the efferent duct and the cauda epididymidis, basolateral addition of AVP resulted in a dose-dependent increase in the short-circuit current (Isc), which was mediated via V1 receptor. Replacement of ambient Cl- with gluconate or pretreatment of a Cl- channel blocker, diphenylamine-2-carboxylate (apical, 1 mM), completely abolished the response, whereas addition of amiloride had no effect on the Isc. Pretreating the epithelia of the efferent duct with indomethacin (apical, 5 microM) or forskolin (basolateral, 1 microM), but not thapsigargin (apical, 1 microM) or trifluoperazine (apical, 20 microM), significantly inhibited the AVP response (P < 0.001). By comparison, pretreating the epithelia of the cauda epididymidis with any of the four agents significantly reduced the AVP-evoked response. These results suggested that the stimulation of chloride secretion by AVP in the efferent duct and the cauda epididymidis is mediated by prostaglandin synthesis and involves adenosine 3',5'-cyclic monophosphate (cAMP) as a second messenger. In the cauda epididymidis, calcium, in addition to cAMP, may play a role in mediating the AVP-induced response.

Effect of intratesticular administration of anti-corticotropin-releasing factor antiserum (a-CRF) on testicular function in neonatal rats

The possible physiological role of testicular corticotropin-releasing factor (CRF) in the regulation of testicular functions was studied in neonatal rats. Two microlitres of anti-CRF-antiserum (dilution: 1:10 or 1:100) was injected intratesticularly to 5 d-old rats with two testes and to hemicastrates. Five days after hemicastration and treatment of the remaining testis with the antiserum, serum testosterone concentration and basal testosterone secretion in vitro decreased significantly. Unilateral testicular injection of a-CRF in rats with two testes resulted in a significant drop in serum testosterone level with no change in basal testosterone production. Data indicate that in neonatal rats testicular CRF might be a local stimulator of steroidogenesis.

Arginine vasopressin- and oxytocin-like peptides in the testis of two Australian marsupials

High performance liquid chromatography (HPLC) and specific radioimmunoassay (RIA) for arginine vasopressin (AVP), mesotocin (MT), and oxytocin (OT) were used to identify and quantify these peptides in the testis of the brushtail possum (Trichosurus vulpecula) and the northern brown bandicoot (Isoodon macrourus). Arginine vasopressin (0.092 +/- 0.041 ng/g) and MT (0.198 +/- 0.089 ng/g), but not OT, were found in the possum testis, while the bandicoot testis contained AVP (0.061 ng/g), MT (0.108 +/- 0.024 ng/g), and OT (0.114 +/- 0.053 ng/g). The values correlate well with those reported for AVP- and OT-like peptides in the testis of eutherian mammals. It was concluded that there are neurohypophysial peptides present in the marsupial testis.

Oxytocin and estradiol concentrations in follicular fluid as a means for the classification of large bovine follicles

Large antral follicles (13 to 20 mm in diameter) were collected from ovaries of 109 cows and 17 heifers that also had a regressed corpus luteum at slaughter. Thirty percent of the animals had been injected once with prostaglandin F(2)alpha 48 hours before slaughter. Follicles were divided into 3 groups based on estradiol and oxytocin concentrations in the follicular fluid: Group I follicles, estradiol>/=100 ng/ml and oxytocin<65 pg/ml (preovulatory and assumed pre-gonadotropin surge); Group II follicles, estradiol<100 ng/ml and oxytocin>/=65 pg/ml (preovulatory and assumed post-gonadotropin surge); and Group III follicles, estradiol<100 ng/ml and oxytocin<65 pg/ml (atretic follicles). Treatment with prostaglandin F(2)alpha significantly increased the number of viable granulosa cells and estradiol content in Group I follicles. The estradiol: progesterone ratio was significantly higher in Group I vs Groups II and III, but it was similar for Group II healthy follicles and Group III atretic follicles. To ascertain the classification of follicles, PGF(2)alpha was administered on Day 6 of the cycle to induce corpus luteum regression, and a GnRH analog was administered 24 hours later. At 23 hours after GnRH analog treatment, follicular oxytocin levels significantly rose to 103 pg/ml. Concomitantly, estradiol concentrations fell to below 100 ng/ml. This response was not evident by 13 h after injection of the GnRH analog. The results indicate that follicular estradiol and oxytocin concentrations may be used as a means for the physiological classification of large bovine follicles.

Local control of Leydig cell arginine vasopressin receptor by naloxone

Arginine vasopressin (AVP) and beta-endorphin are present within the testis where they could act as paracrine effectors of steroidogenesis. In this study we investigated the effect of naloxone, an opioid receptor antagonist on Leydig cell AVP receptor. Intratesticular injection of increasing doses of naloxone (0.1-100 micrograms) resulted 24 h later in a dose-dependent increase in Leydig cell AVP binding capacity. This effect occurred locally since s.c. injection of similar doses of naloxone did not alter the testicular AVP receptor content and intratesticular injection enhanced AVP receptor density only in the naloxone-treated testis but not in the contralateral vehicle-treated testis. Scatchard plot analysis of the data revealed that naloxone locally injected altered AVP binding capacity without change in affinity. These results suggest that in addition to their known paracrine effects in the testis, endogenous opioid peptides may locally control the testicular AVP system by modulating AVP receptor capacity.

In vitro effects of arginine vasotocin on testosterone production by testes of rainbow trout (Oncorhynchus mykiss)

The objective of this study was to investigate the effect of arginine vasotocin (AVT) on testosterone (T2) production by the rainbow trout testis in culture. AVT increased T2 production in a dose-dependent manner in immature testes. The maximum response (10 nM AVT) increased T2 production 6-fold over basal (3-6 pg/mg tissue protein). Mature testes did not respond to AVT. Salmon gonadotropin (2.5 nM sGtH, SGA-GtH) stimulated T2 production by both juvenile (5-fold) and mature (11-fold) testes. When AVT (100 nM) was added in addition to salmon gonadotropin (sGtH; from 0.1 to 100 nM), AVT had a stimulatory effect at the submaximal doses of sGtH, but T2 production did not exceed the maximum level obtained with sGtH (100 nM) alone. Isotocin also increased T2 production although to a lesser degree than AVT. The maximum response at 10 nM increased T2 production 4-fold over basal. beta-Endorphin had no effect on T2 production.

Regulation of the testis

The testicular cells are regulated by factors produced locally in the testis. These factors include peptide growth factors, pro-opiomelanocortin derivatives, neuropeptides and steroids. Several agents able to affect steroido- and spermatogenesis can also affect leukocytes and many of the testis-regulating factors are produced by immune cells, suggesting that testicular cells and leukocytes may interact. In the present article, the effects of various testicular cell and leukocyte produced factors on steroido- and spermatogenesis are reviewed. The possibility that leukocytes may produce substances able to affect the testicular functions suggests that inhibition of immune system activation in the testis may be important also for reasons other than protection of autoantigenic germ cells from an autoimmune attack.

Arginine vasotocin and mesotocin levels in theca and granulosa layers of the ovary during the oviposition cycle in hens (Gallus domesticus)

Neurohypophysial hormones in mammals are synthesized by the ovary and may influence reproductive function. Although arginine vasotocin (AVT) can induce premature oviposition in chickens, the gonadal content of AVT or mesotocin (MT) has not been examined in this species. Ovarian follicles were removed 2 hr before oviposition (-2 hr), immediately after oviposition (0 hr), and 5 hr after oviposition (+5 hr). The theca and granulosa layers of the three largest preovulatory and postovulatory follicles were isolated, extracted, and assayed for immunoreactive AVT and MT. AVT content in the theca and granulosa layers was lowest at -2 hr and increased to maximum levels at +5 hr. Pre- and postovulatory follices contained similar amounts of AVT. Maximum AVT levels in the theca and granulosa layers were 2.5 +/- 0.6 and 1.3 +/- 0.2 ng/tissue, respectively. In contrast, theca content of MT was maximal at 0 hr and the highest peptide levels were observed in the largest preovulatory follicle (0.24 +/- 0.02 ng/tissue). The results demonstrate that, compared with circulating levels of the hormones, the ovary of the chicken contains high concentrations of AVT and MT. The ovarian content of AVT and MT varies in a different manner in relation to the oviposition cycle.

Vasopressin antagonist in early postoperative diabetes insipidus

23 patients without diabetes insipidus before transfrontal (hypothalamic) or trans-sphenoidal (pituitary) surgery were studied prospectively to investigate the pathogenesis of early postoperative diabetes insipidus. 12 patients who underwent trans-sphenoidal surgery and who did not develop diabetes insipidus were used as controls. All received prophylactic corticosteroid replacement. Blood samples were obtained immediately after operation, at the onset of diabetes insipidus, and 24 h later. Immediately after trans-sphenoidal pituitary surgery, plasma vasopressin (AVP) was raised but had fallen to subnormal concentrations by the onset of diabetes insipidus. After transfrontal hypothalamic surgery diabetes insipidus occurred sooner and was associated with high plasma AVP immunoreactivity--but the plasma showed no antidiuretic bioactivity and greatly attenuated the antidiuretic response to standard AVP. Early diabetes insipidus after hypothalamic surgery is associated with release of a substance, presumably an analogue, from the damaged hypothalamo-neurohypophyseal system, which acts as an antagonist to normal AVP activity; after trans-sphenoidal operations diabetes insipidus seems to be caused by failure of AVP release.

Hypothalamic modulation of immunoreactive oxytocin in the rat thymus

Immunoreactive oxytocin was determined in a peptidic extract of rat thymus by means of a highly specific radioimmunoassay combined with high pressure liquid chromatography fractionation. Rat thymus was found to contain 80 +/- 7.5 pg/g wet tissue (congruent to 0.56 pg/mg protein) of oxytocin-like immunoreactivity, which behaved like synthetic oxytocin in the radioimmunoassay and in two different high pressure liquid chromatography columns. Oxytocin concentration was increased by bilateral electrolytic lesion of the paraventricular nucleus of the hypothalamus (PVN), and by high doses of corticosterone (10 mg/kg IM for 7 days) but was not modified by low doses of corticosterone (1 mg/kg IM for 7 days) or by hypophysectomy. The results suggest that rat thymus synthesizes oxytocin and that thymic oxytocin concentration is modulated by the hypothalamus.

Central vasopressin raises arterial pressure by sympathetic activation and vasopressin release

Although central administration of arginine vasopressin (AVP) has been reported to increase arterial pressure mediated by activation of the sympathetic system, we found that peripheral blockade of sympathetic transmission did not attenuate this pressor response. To elucidate the mechanism, rats were pretreated with either phentolamine (3 mg/kg), chlorisondamine (2.5 mg/kg), a vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)AVP (AVP-X) (10 micrograms/kg), or the combinations of phentolamine and AVP-X or chlorisondamine and AVP-X. The pressor response to intracerebroventricular injection of AVP in unrestrained conscious rats was reduced but not significantly altered by intravenous injection of phentolamine or AVP-X; however, combined treatment with these agents abolished the response. To determine that the amount of central AVP leaked to the periphery did not contribute to the pressor effect, tritiated AVP and AVP (100 ng total) were injected intracerebroventricularly. Blood samples collected at 0, 3, and 30 minutes after injection showed that radioactivity in plasma was primarily metabolites and that the amount of intact AVP estimated to leak from the brain was too low to produce a pressor effect. Comparative regional hemodynamic studies between intracerebroventricular and intravenous injection of AVP performed in conscious rats instrumented with Doppler flow probes demonstrated a qualitatively similar pattern of increased resistance in the renal, mesenteric, and hindquarters beds. These data suggest that central pressor action of AVP is mediated by both activation of the sympathetic system and release of AVP.

Presence and actions of vasopressin-like peptides in the rabbit anterior uvea

The presence of vasopressin-like immunoreactivity (VP-IR) in the rabbit eye was demonstrated by radioimmunoassay. Trigeminal nerve denervation resulted in a significant and selective decrease in the levels of VP-IR in the iris sphincter muscle and the cornea. The isolated iris sphincter muscle contracted in response to low concentrations of [Arg8]vasopressin (AVP) and related peptides. The V1 vasopressin receptor antagonist, d(CH2)5Tyr(Me)AVP, potently inhibited the contractile responses to AVP. AVP was found to induce an increase in the accumulation of inositol phosphates in the iris sphincter muscle but not in the dilator/ciliary body preparation in vitro. The present investigation demonstrates the presence of VP-IR in the rabbit eye and that this substance may be another sensory nerve-derived mediator acting on specific target sites in the anterior uvea.

Arginine vasopressin stimulates phosphoinositide turnover in an enriched rat Leydig cell preparation

An enriched rat Leydig cell preparation was preincubated with [14C]arachidonic acid. Stimulation of the cells with arginine vasopressin (AVP) (1 microM) for 2 min caused a significant increase in labelled phosphatidic acid and a significant fall in radioactivity in phosphatidylinositol and phosphatidylinositol 4-monophosphate + phosphatidylinositol 4,5-bisphosphate. Preincubation with dibutyryl cyclic AMP had no effect on the AVP-induced phospholipid turnover. Leydig cells were preincubated with myo-[2-3]inositol for 22 h and then with 10 mM LiCl for 10 min. Exposure to AVP (1 microM) induced a rise in labelled inositol phosphates. The response was inhibited when the cells were preincubated with the phorbol ester, 4 beta-phorbol 12-myristate 13-acetate (0.16 microM) for 10 min. These results provide evidence for an AVP-induced phospholipase C stimulation in rat Leydig cells and suggest a protein kinase C-dependent feedback inhibition of the stimulation. Other agonists that might have a regulatory function in the testis were tested for possible effects on phosphoinositide metabolism. Of prostaglandin E2 (10 microns,) angiotensin II (0.1 microM), and bradykinin (0.9 microM), only the latter induced a significant increase in the labelled inositol phosphates. This suggests that Leydig cells possess a bradykinin receptor which can activate phospholipase C.

Identification and characterization of arginine vasopressin receptors in the clonal murine Leydig-derived TM3 cell line

Specific arginine vasopressin (AVP) binding sites were identified and characterized using Leydig cell membranes prepared from a clonal murine Leydig-derived cell line, TM3. 3H-AVP binding data analyses demonstrated that the radioligand binds to a high affinity, low capacity, homogeneous class of sites with a dissociation constant of 0.5 nM. Characterization of these AVP binding sites included competition studies. Displacement of 3H-AVP binding with high affinity by unlabelled AVP, LVP and the V1 antagonist, d(CH2)5Tyr(Me)AVP, indicated that the Leydig cell AVP receptor is of the V1 type. Furthermore, AVP did not increase adenylate cyclase activity in TM3 membranes, a finding consistent with the V1 type of AVP receptor. No competition with 3H-AVP was found with the V2 agonist, dVDAVP, or the selective oxytocin agonist, [Thr4,Gly7]oxytocin. No specific binding for oxytocin was found in Leydig cell membranes. No specific binding for either 3H-AVP or 3H-oxytocin was observed in membranes prepared from the Sertoli cell line or peritubular cell line. These findings indicate that murine Leydig cells have specific AVP binding sites of the V1 type. These AVP sites are not coupled to the adenylate cyclase system.

Ectopic hormone production

Current understanding of the phenomenon of ectopic hormone production is largely based on a histopathological and immunocytochemical analysis of peptide hormone secreting tumours arising in non-endocrine tissues. Recent advances in the study of gene regulation show that the tissue-specific expression of genes is a highly sophisticated process and is unlikely to be disturbed by a spontaneous event such as point mutation in DNA. Study of several genes for frequently found ectopic hormones, i.e. prop-opiomelanocortin, vasopressin/neurophysin II, gastrin-releasing peptide, parathyroid hormone-related peptide, calcitonin gene-related peptide and beta-chorionic gonadotropin, suggests they are transcribed as they would be in their natural cell of origin. It is argued therefore that these data are compatible with the concept that the tumour cell of origin was capable of expressing these peptides, if only in a minor or transient manner. In one example, the ectopic ACTH syndrome, it is also necessary to explain the non-suppression of this gene's expression by elevated levels of glucocorticoids. Recent work suggests that this may result from physically present, but biologically inactive glucocorticoid receptors, a phenomenon that has occasionally been noted in hormonally inactive tumour tissue and cell lines.

Oxytocin and vasopressin are present in human and rat pancreas

Immunoreactive oxytocin and vasopressin were found in human and rat pancreatic extracts. The pancreatic oxytocin and vasopressin eluted on Sephadex G-75 gel filtration chromatography and on reverse phase high pressure liquid chromatography in the same positions as their respective reference preparations. The immunoreactive oxytocin was biologically active in the rat milk ejection assay. The presence of oxytocin and vasopressin in human and rat pancreatic extracts suggests the possibility of local synthesis of both hormones. The neurohypophysial hormones are known to be endocrine mediators of insulin and glucagon release. The finding of oxytocin and vasopressin in the pancreas raises the possibility, although yet unproven, of local synthesis and perhaps a paracrine function for the neurohypophysial peptides upon pancreatic hormone release or for a local function upon the liver.

Distribution of immunoreactive vasotocin and mesotocin in the chicken gastrointestinal tract

Immunoreactive arginine vasotocin (AVT) and mesotocin (MT) were measured in heart, breast muscle, adrenals, testes, and different parts of the gastrointestinal tract in adult male chickens. Neither of the peptides were detected in liver, testis, heart and breast muscle. The amounts of AVT and MT in the adrenals were 167 +/- 25 and 669 +/- 198 pg/gland, respectively. Considerable amounts of immunoreactive peptides were found in the gastrointestinal tract with the highest concentration in the proventriculus (4.18 +/- 0.31 ng AVT and 16.58 +/- 0.86 ng MT per organ). Dose-response curves of duodenal and proventriculus extracts were parallel with synthetic AVT and MT standards.

A day/night rhythm of vasopressin and oxytocin in rat retina, pineal and harderian gland

Arginine vasopressin (AVP), oxytocin (OT) and neurophysins (Np) have been found in the pineal gland and the retina of the rat. Because the retina, pineal gland and Harderian gland (HG) serve analogous functions, we undertook a study to determine the presence of these peptides in these three organs of rats. They were detected by two specific methods: HPLC and specific radioimmunoassays. For Np, total neurophysins (NpT) were measured. To determine a 24 hr rhythm, the animals were maintained under a light/dark cycle of 12 hr/12 hr for 3 weeks. The pineal glands, retinae and HG were collected. Day/night rhythms of AVP, OT and NpT were demonstrated in the retina and HG; but the pineal gland had only AVP rhythm. A significant decrease in the rhythms at 4 a.m. was demonstrated in the retina and HG. The 24 hr variation of AVP in the retina seemed parallel to that of the HG.

Modulation of mouse Leydig cell steroidogenesis through a specific arginine-vasopressin receptor

Characterization of specific vasopressin binding sites was investigated in purified mouse Leydig cells using tritiated arginine-vasopressin. Binding of radioligand was saturable, time- and temperature-dependent and reversible. (3H)-AVP was found to bind to a single class of sites with high affinity (Kd = 2.20 +/- 0.18 nM) and low capacity (Bmax = 17.4 +/- 1.8 fmol/10(6) Leydig cells). Binding displacements with specific selective analogs of AVP indicated the presence of V1 subtype receptors on Leydig cells. The ability of AVP to displace (3H)-AVP binding was greater than LVP and oxytocin. The unrelated peptides, somatostatin and substance P, were less potent, while neurotensin and LHRH did not displace (3H)-AVP binding. The time-course effects of AVP-pretreatment on basal and hCG-stimulated testosterone and cAMP accumulations were studied in primary culture of Leydig cells. Basal testosterone accumulation was significantly increased by a 24 h AVP-pretreatment of Leydig cells (P less than 0.001). This effect was potentiated by the phosphodiesterase inhibitor (MIX) and was concomitantly accompanied by a slight but significant increase in cAMP accumulation (P less than 0.01). AVP-pretreatment of the cells for 72 h had no effect on basal testosterone accumulation, but exerted a marked inhibitory effect on the hCG-stimulated testosterone accumulation (P less than 0.001). This reduction of testosterone accumulation occurred even in the presence of MIX and was not accompanied by any significant change of cAMP levels. We conclude from these data that AVP is capable of modulating steroidogenesis in Leydig cells through specific and functionally V1 receptor subtype and postulate that this effect may be part of an intratesticular paracrine/autocrine control mechanism.

Arginine-vasopressin stimulates the formation of phosphatidic acid in rat Leydig cells

Arginine-vasopressin (AVP) stimulated the formation of labelled phosphatidic acid (PA) in [14C]arachidonic acid-prelabelled rat Leydig cells. After addition of 10(-6)M AVP [14C]arachidonoylphosphatidic acid reached a maximum within 2 min. The increase was dose-dependent (10(-11)-10(-6)M). No change in labelling of other phospholipids and diacylglycerol could be detected. The V1 antagonist dPTyr(Me)AVP inhibited in a dose-dependent manner the AVP-stimulated accumulation of PA. The V2 agonist dPVDAVP was without effect. The present results suggest that AVP binds to V1 receptors in rat Leydig cells resulting in stimulation of PA turnover. We suggest that the AVP-stimulated PA formation is an indication of phosphoinositide turnover.

Intragonadal control mechanisms

On the weight of the evidence presented above, it is concluded that regulation at a local, intragonadal level is an integral part of the overall regulation of gonadal function in both sexes. The interaction between cells within a gonad extends beyond the same cell type to include germ cell-somatic cell interactions as well. We believe this local interaction between cell types facilitates the differing requirements of the various developmental stages of germ cells within the gonad, which would not be possible by simply varying the afferent pituitary hormone supply. We re-emphasize that the local factors responsible for these interactions are acting in conjunction with the pituitary hormones, and, in some cases, may be their proximate regulators. A more controversial phenomenon is the possibility of an interaction between the gonads which does not involve the hypothalamic-pituitary axis. The little evidence which is available to support this hypothesis comes mainly from studies on ovarian function, particularly recruitment and selection of follicles. More research on this phenomenon is warranted. Not surprisingly there are many parallels between the testes and ovaries with respect to the nature and action of local regulators. For example, the intragonadal action of steroids, the local modulation of the response of target cells to FSH, the influence of macrophages on steroidogenesis and the presence of mitotic and meiotic regulators are common to both sexes. It would not be surprising if the chemical nature of these factors in the ovary and testes are similar. If the ever-increasing list of factors and activities being discovered in the gonads is any guide, the phenomena outlined in this review are just the beginning of an extensive list of cell-cell interactions occurring within and between the gonads. No doubt the gonads will share with other organs the same interactions between cells which are required for normal cellular function. The uniqueness of the gonads lies in their protection and production of germ cells. The challenge of the future for reproductive biologists will be to discover and describe the interactions within and between germ cells which are obligatory for normal reproductive function, and to apply that information to devising ways of overcoming infertility and regulating fertility.