Immunohistochemical localization of oxytocin and vasopressin in the adrenal glands of rat, cow, hamster and guinea pig

The Importance of Experimental Investigation of the Peripheral Oxytocin System

Oxytocin and oxytocin receptors are synthesized in the periphery where paracrine/autocrine actions have been described alongside endocrine actions effected by central release of oxytocin from the posterior pituitary. In the female reproductive system, classical actions of uterine contraction and milk ejection from mammary glands are accompanied by actions in the ovaries where roles in steroidogenesis, follicle recruitment and ovulation have been described. Steroidogenesis, contractile activity, and gamete health are similarly affected by oxytocin in the male reproductive tract. In the cardiovascular system, a local oxytocinergic system appears to play an important cardio-protective role. This role is likely associated with emerging evidence that peripheral oxytocin is an important hormone in the endocrinology of glucose homeostasis due to its actions in adipose, the pancreas, and the largely ignored oxytocinergic systems of the adrenal glands and liver. Gene polymorphisms are shown to be associated with a number of reported traits, not least factors associated with metabolic syndrome.

The role of oxytocin and vasopressin in the pathophysiology of heart failure in pregnancy and in fetal and neonatal life

Pregnancy and early life create specific psychosomatic challenges for the mother and child, such as changes in hemodynamics, resetting of the water-electrolyte balance, hypoxia, pain, and stress, that all play an important role in the regulation of the release of oxytocin and vasopressin. Both of these hormones regulate the water-electrolyte balance and cardiovascular functions, maturation of the cardiovascular system, and cardiovascular responses to stress. These aspects may be of particular importance in a state of emergency, such as hypertension in the mother or severe heart failure in the child. In this review, we draw attention to a broad spectrum of actions exerted by oxytocin and vasopressin in the pregnant mother and the offspring during early life. To this end, we discuss the following topics: 1) regulation of the secretion of oxytocin and vasopressin and expression of their receptors in the pregnant mother and child, 2) direct and indirect effects of oxytocin and vasopressin on the cardiovascular system in the healthy mother and fetus, and 3) positive and negative consequences of altered secretion of oxytocin and vasopressin in the mother with cardiovascular pathology and in the progeny with heart failure. The present survey provides evidence that moderate stimulation of the oxytocin and vasopressin receptors plays a beneficial role in the healthy pregnant mother and fetus; however, under pathophysiological conditions the inappropriate action of these hormones exerts several negative effects on the cardiovascular system of the mother and progeny and may potentially contribute to the pathophysiology of heart failure in early life.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

Effects of vasopressin on isolated rat adrenal chromaffin cells

It has been demonstrated that arginine vasopressin (AVP) is synthesized not only in specific hypothalamic nuclei, but also in the adrenal medulla where it is thought to regulate adrenal functions by autocrine and paracrine mechanisms. In order to further characterise the effects of AVP on rat adrenal chromaffin cells, we examined: (a) the mRNA expression for V(1a) and V(1b) AVP receptors in these cells; (b) the effects of AVP on the membrane potential and membrane currents measured with the whole-cell patch-clamp technique; and (c) effect of AVP on catecholamine release from single adrenal chromaffin cells measured with carbon fibre microelectrodes. Reverse transcription-polymerase chain reaction (RT-PCR) on tissue punch samples obtained from the adrenal medulla demonstrated message for both the V(1a) and V(1b) receptors, while material obtained from the adrenal cortex showed expression of the V(1a) receptor only. Single-cell RT-PCR conducted on acutely isolated chromaffin cells showed message for the V(1a) receptor in 84% of cells, while 38% of cells also contained message for the V(1b) receptor (n=45). Under current-clamp recording, responses to AVP application (4-40 microM) were variable; 22/34 (65%) tested cells were depolarised, 29% hyperpolarised, and the remaining cells showed a biphasic response. Changes in membrane potential of either direction were dose-dependent and accompanied by a decrease in cell membrane resistance. Under voltage-clamp (V(hold)=-60 mV), AVP evoked inward current in 27/52 (52%) and outward current in 16/52 (31%) chromaffin cells. Both types of AVP-evoked responses were blocked by co-application of a nonselective V(1a)/V(1b) antagonist. Application of AVP evoked prolonged bursts of amperometric currents (indicative of catecholamine release) in 4/9 tested cells, but reduced the currents evoked by ACh application in all tested cells (n=7). These findings demonstrate a complex action of AVP on adrenal chromaffin cells, with individual adrenal chromaffin cells responding with either excitation or inhibition. This response pattern may be related to the expression of V(1) receptor subtypes.

The oxytocin receptor system: structure, function, and regulation

The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via G(q) proteins to phospholipase C-beta. The high-affinity receptor state requires both Mg(2+) and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has been characterized by mutagenesis and molecular modeling and is different from the antagonist binding site. The function and physiological regulation of the OT system is strongly steroid dependent. However, this is, unexpectedly, only partially reflected by the promoter sequences in the OT receptor gene. The classical actions of OT are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation. While the essential role of OT for the milk let-down reflex has been confirmed in OT-deficient mice, OT's role in parturition is obviously more complex. Before the onset of labor, uterine sensitivity to OT markedly increases concomitant with a strong upregulation of OT receptors in the myometrium and, to a lesser extent, in the decidua where OT stimulates the release of PGF(2 alpha). Experiments with transgenic mice suggest that OT acts as a luteotrophic hormone opposing the luteolytic action of PGF(2 alpha). Thus, to initiate labor, it might be essential to generate sufficient PGF(2 alpha) to overcome the luteotrophic action of OT in late gestation. OT also plays an important role in many other reproduction-related functions, such as control of the estrous cycle length, follicle luteinization in the ovary, and ovarian steroidogenesis. In the male, OT is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. OT receptors have also been identified in other tissues, including the kidney, heart, thymus, pancreas, and adipocytes. For example, in the rat, OT is a cardiovascular hormone acting in concert with atrial natriuretic peptide to induce natriuresis and kaliuresis. The central actions of OT range from the modulation of the neuroendocrine reflexes to the establishment of complex social and bonding behaviors related to the reproduction and care of the offspring. OT exerts potent antistress effects that may facilitate pair bonds. Overall, the regulation by gonadal and adrenal steroids is one of the most remarkable features of the OT system and is, unfortunately, the least understood. One has to conclude that the physiological regulation of the OT system will remain puzzling as long as the molecular mechanisms of genomic and nongenomic actions of steroids have not been clarified.

Species- and tissue-specific physiological regulation of vasopressin mRNA poly(A) tail length

Transgenic experiments can be used to test the extent to which genes from different species can be swapped around, but still retain function, and be appropriately regulated. A vector has been developed that directs the expression of foreign genes to specific groups of vasopressin (VP) hypothalamic neurons in transgenic rats. Using this vector, we have expressed the bovine VP (bVP) RNA in the rat brain. In contrast to the situation in a mouse host, but like its endogenous rat counterpart, the mRNA encoded by the bVP transgene is subject to posttranscriptional physiological regulation in the hypothalamus; its poly(A) tail dramatically lengthens as a consequence of 3 days of dehydration. Transgene expression is also seen in the adrenal cortex, but here, despite a marked increase in transgene RNA levels with dehydration, there is no change in poly(A) tail length. These data suggest that the mouse hypothalamus and the rat adrenal gland do not have the transcript recognition or enzymatic machinery required for the physiologically responsive poly(A) tail length modulation seen in the rat brain.

Functional histology of the neuroendocrine thymus

The primary role of the thymus lies in T-cell differentiation and self-education leading to the establishment of appropriate host immune defenses. However, the view of the thymus as a self-contained organ is no longer valid. It is now clear that intricate interactions of both a stimulatory and inhibitory nature exist between the neuroendocrine and immune system. A broad array of neuroendocrine circuits are networked with the thymus and neuroendocrine-thymic interactions are bidirectional. These interactions are thought to play an important immunomodulatory role during an active immune response, during T-cell ontogeny and in the aging process of the whole organism. The chemical messengers that transmit communicating signals in this network are secreted neuropeptides and their specific receptors. The objective of this review is to provide a comprehensive overview of the morphological substrates of these neuropeptides in the thymus.

Arginine-vasopressin stimulates CRH and ACTH release by rat adrenal medulla, acting via the V1 receptor subtype and a protein kinase C-dependent pathway

Arginine-vasopressin (AVP) is a hypothalamic hormone that, like CRH, stimulates the pituitary release of ACTH, thereby activating adrenal glucocorticoid secretion. Evidence indicates that rat adrenal medulla contains a CRH-ACTH system duplicating that existing at the hypothalamo-pituitary level and involved in the paracrine stimulation of the cortex secretion. Therefore, we investigated by RIA the effect of AVP on the release of CRH and ACTH immunoreactivities (IR) by rat adrenal medulla in vitro. AVP concentration-dependently enhanced the release of both CRH-IR and ACTH-IR, and the effect was blocked by a selective antagonist of the V1 subtype of AVP receptors. The CRH receptor antagonist alpha-helical-CRH partially reversed AVP-evoked rise in ACTH-IR release, without altering either CRH response or basal secretions of CRH and ACTH. The specific inhibitors of protein kinase C Ro31-8220 and calphostin C abolished both CRH and ACTH responses to AVP. In conclusion, our present findings suggest that AVP stimulates intramedullary the CRH-ACTH system, acting via V1 receptors and activating protein kinase C.

Effects of oxytocin on the function and morphology of the rat adrenal cortex: in vitro and in vivo investigations

The effects of oxytocin (OX) on the function and morphology of the rat adrenal cortex were studied in vivo and in vitro. OX exerted a potent stimulatory action on basal, but not 10(-8) M ACTH-stimulated corticosterone (B) secretion of dispersed rat inner (zona fasciculata and zona reticularis) adrenocortical cells (maximal effective concentration: 10(-9) M); in contrast, at higher concentrations (10(-7)/10(-6) M) OX inhibited maximally ACTH-stimulated B output. A single subcutaneous (s.c.) injection of 1.2 nmol/100 g body weight OX resulted in a long-lasting (up to 12 h) rise in plasma B concentration (PBC). The prolonged administration of OX (daily s.c. injections of 0.6 or 1.2 nmol/100 g for 10 days) caused a marked lowering in the adrenal weight and volume of all adrenocortical zones, that in turn was due to a decrease in the number of their parenchymal cells; however, the average volume of inner adrenocortical cells was significantly increased. Basal PBC was lowered, but its response to ether stress was unchanged in comparison with control rats. Prolonged OX treatment did not change B secretion by adrenal slices, but it markedly raised that of dispersed inner adrenocortical cells. Our present findings clearly show that the effects of OX on the adrenal cortex depend on the experimental model employed (in vitro versus in vivo) and the duration of treatment (acute versus chronic). Taken together they allow us to conclude that OX exerts an acute direct stimulatory effect on the rat adrenal cortex, and a chronic inhibitory one, that at least in part could be due to the interference of OX with the mechanism(s) of intracellular transduction of the ACTH secretagogue signal.

Oxytocin-producing and vasopressin-producing eosinophils in the mouse spleen: immunohistochemical, immuno-electron-microscopic and in situ hybridization studies

Oxytocin-like and vasopressin-like immunoreactive cells, and the cells expressing mRNAs for these peptides in the spleen of the C57BL/6 mouse were studied by immunohistochemistry, immuno-electron microscopy and in situ hybridization. Immunoreactive cells were distributed mainly in the splenic cord and marginal zone, whereas there were few in the lymphocyte-packed periarteriolar-lymphoid sheath, lymphoid follicle and germinal center. More numerous vasopressin-positive cells were seen in the splenic cord. The colocalization of oxytocin-like and vasopressin-like immunoreactivity in the same cells was identified by the investigation of mirror sections. By the pre-embedding immuno-electron-microscopic method using antisera against oxytocin and vasopressin, immunopositive reaction products were localized in the matrix around the specific granules, small clear vesicles and mitochondrial membrane of the eosinophils. No immunoreactivity to these peptides was found within the specific granules of the eosinophils. In situ hybridization with synthetic oligonucleotide probes labeled with 32P revealed the presence of mRNAs for oxytocin and vasopressin in the cells of the spleen, the distribution of the mRNAs for these peptides being the same as that of immunopositive cells. These observations suggest that eosinophils synthesize both oxytocin and vasopressin and store them in the matrix. Possible differences in the mechanism of synthesis and storage of these peptides between peripheral eosinophils and hypothalamic neurons are discussed.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

Acetylcholine induces oscillations in intracellular calcium in isolated bovine adrenal zona fasciculata/reticularis cells

The effects of acetylcholine (ACh) on intracellular free calcium were studied in primary cultures of purified bovine adrenal zona fasciculata/reticularis (ZFR) cells. In fura-2 loaded single cells, concentrations of ACh which stimulated cortisol secretion and phosphoinositol production were found to promote an increase in free cytosolic calcium ([Ca2+]i). This response was heterogeneous, showing either (i) an initial increase in [Ca2+]i followed by a fall to a level above that in unstimulated cells, or (ii) an initial increase followed by oscillations about the original resting level or a higher resting level. The frequencies of [Ca2+]i oscillations to ACh showed a dose-dependent trend. The sustained [Ca2+]i oscillations were abolished by the muscarinic antagonist atropine, or by removal of extracellular Ca2+. These data demonstrate for the first time in adrenocortical cells that: (i) ACh can induce [Ca2+]i oscillations in single ZFR cells; (ii) these oscillations occur in a dose-dependent manner; (iii) the sustained oscillatory phase is dependent on influx of extracellular Ca2+. Thus, like cells of the zona glomerulosa, bovine ZFR cells are also capable of sustained dose-dependent oscillatory responses to agonists which activate phosphoinositidase C.

Posterior pituitary of the newborn marsupial possum, Trichosurus vulpecula

The fetal anterior pituitary-adrenal axis is thought to be involved in the initiation of birth in both eutherian and marsupial mammals. Little is known about the structure and function of the posterior pituitary at birth in the marsupial. Immunocytochemistry, high pressure liquid chromatography, and radioimmunoassay were used to identify vasopressin and mesotocin in the posterior pituitary of a newborn marsupial, the brushtail possum, Trichosurus vulpecula. The concentrations of vasopressin and mesotocin in the head of the newborn possum were 0.34 and 0.28 ng, respectively. The concentration of vasopressin was always greater than that of mesotocin, and the amounts of neuropeptides present in the head increased as the possum developed.

Transgenic mouse models of vasopressin expression

Arginine vasopressin is a nine-amino acid neuropeptide hormone important in the regulation of water metabolism. It also may have a role in other physiological functions, such as blood pressure regulation and the response to stress. Whole animal studies have provided a good understanding of vasopressin physiology and regulation of the normal vasopressin gene, and in vitro cell culture studies have demonstrated important features of the intracellular regulation of vasopressin gene expression. Transgenic mice provide useful models for the study of the in vivo regulation of gene expression. Previously reported mouse lines transgenic with vasopressin gene constructs have not expressed the transgene in a tissue distribution similar to that detected for the endogenous mouse vasopressin gene. An 8.2-kb genomic construct of the rat vasopressin gene, including 3 kb each of 5' and 3' flanking sequences, has been used to develop a line of transgenic mice. These animals express the transgene in a tissue-specific manner, demonstrate appropriate osmotic regulation of transgenic vasopressin mRNA, and have normal water metabolism. Animals homozygous for the 8.2-kb transgene have increased basal plasma levels of vasopressin peptide but have no apparent change in basal water metabolism. The findings with this and other previously reported mouse lines transgenic for vasopressin constructs provide a basis for developing future transgenic lines to study the in vivo regulation of the vasopressin gene.

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.

Immunohistochemical evidence for the presence of oxytocin in the opossum corpus luteum

Corpora lutea from opossums late in pregnancy were examined by immunohistochemistry for the presence of oxytocin. Oxytocin-immunoreactivity was observed in all corpora lutea examined but not elsewhere in ovarian tissue. The immunoreactive staining observed was confined primarily to the perinuclear cytoplasm of reactive luteal cells. Not all luteal cells showed oxytocin-immunoreactivity. The immunohistochemical localization of oxytocin in the pregnant opossum corpus luteum demonstrates for the first time this peptide in a metatherian ovary. Its presence in this primitive species suggests that oxytocin has a fundamental role in the physiology of the mammalian ovary.

Mesotocin and oxytocin in the brain and plasma of an australian marsupial, the northern brown bandicoot, isoodon macrourus

1. Mesotocin (MT) and oxytocin (OT) were measured in the brain and plasma of bandicoots using reverse phase high performance liquid chromatography and specific radioimmunoassays. 2. MT and OT were found in the pituitary (1.25 +/- 0.10 micrograms/MT; 0.725 +/- 0.077 micrograms/OT) and hypothalamus (38.37 +/- 6.46 ng/MT; 19.1 +/- 4.61 ng/OT). Smaller amounts were present in the cerebral cortex. 3. Basal plasma concentrations ranged from 1.5 to 8.1 pg/ml for both peptides (N = 14) and were elevated by stress. 4. It was concluded that both MT and OT are secreted by the bandicoot brain and that stress stimulates secretion.

Neural influence on oxytocin-induced changes of adrenomedullary catecholamines in the pigeon

Oxytocin (0.25 IU/100 g body wt) was injected intraperitoneally only once to unilaterally splanchnic denervated pigeons. The effects were investigated after 0.5, 4, 12, 24, 72, 144 and 216 h of administration. The findings revealed that oxytocin caused the release of more norepinephrine (NE) from the denervated glands up to 24 h after treatment. In contrast, oxytocin-induced release of epinephrine (E) showed no significant difference in between the innervated and the denervated glands after 0.5 h of treatment. Strikingly, oxytocin brought about release of more E from the denervated glands after 24 h of treatment. This indicates that the first phase of NE release and the second phase of E release are neurally regulated. The findings further revealed that the resynthesis of both NE and E was faster in the innervated glands after 216 h of oxytocin treatment. This clearly points out that the splanchnic nerve accelerates resynthesis of both NE and E induced by oxytocin.

Effects of arginine vasopressin on the pituitary-adrenocortical axis of intact and dexamethasone-suppressed rats

Weekly infusion with arginine vasopressin (AVP) (2 micrograms.kg-1.day-1) exerted a slight stimulatory effect on the adrenal growth of intact female rats and induced a 2-fold rise in plasma aldosterone concentration (PAC), without apparently affecting corticosterone (B) and ACTH secretions. Weekly dexamethasone (Dx) administration (125 micrograms.kg-1.day-1) caused a marked adrenal atrophy, a conspicuous suppression of B and ACTH productions, and a 5-fold increase in PAC. AVP infusion reversed the Dx-induced adrenal atrophy. It did not counteract the suppression of B and ACTH secretions, nor did it change PAC. These findings suggest that chronic AVP treatment is able to stimulate adrenal growth by a Dx-insensitive mechanism (i.e. independent of any change in ACTH secretion). Conversely, AVP may enhance the steroid secretory capacity only in adrenocortical cells in which the maintenance of the steroidogenic machinery is assured by normal levels of circulating ACTH.

Immunocytochemical localization of neuropeptides in the adrenal medulla

The distribution of neuropeptides exhibits pronounced interspecies heterogeneity. Neuropeptides may function as hormones secreted from chromaffin cells or as neurotransmitters/neuromodulators released from nerve terminals. However, other possible functions such as trophic or intracellular effects should also be considered. Thus, to understand the role of neuropeptides, it is important to explore their localization in different species. The distribution of enkephalins, neurotensin, neuropeptide Y, calcitonin gene-related peptide, and galanin in the adrenal medulla of rat, cat, hamster, and mouse is presented in detail.

Immunocytochemical location of oxytocin and mesotocin within the hypothalamus of two Australian marsupials, the bandicoot Isoodon macrourus and the brushtail possum Trichosurus vulpecula

The presence of oxytocin and mesotocin in the hypothalamus of two Australian marsupials, the bandicoot (Isoodon macrourus) and the brushtail possum (Trichosurus vulpecula), was examined by immunocytochemistry. Tissue was fixed in paraformaldehyde in phosphate buffer and immunoreactive cells were detected using highly specific rabbit antioxytocin and sheep anti-mesotocin as primary antisera. Immunoreactive oxytocin cells were demonstrated in the paraventricular and supraoptic nuclei of bandicoot and possum hypothalami, with greater density being observed in paraventricular nuclei. Immunoreactive mesotocin cells were also found in both hypothalamic nuclei of the possum but not of the bandicoot. The same cells appeared to stain for both peptides.

The localization of oxytocin and mesotocin in the reproductive tract of the male marsupial bandicoot Isoodon macrourus

The cellular localization of oxytocin and mesotocin within the testis and prostate of the Northern brown bandicoot, Isoodon macrourus, was examined. Tissues were fixed in 4% paraformaldehyde and immunoreactive cells and tissues were detected with antibodies to oxytocin and mesotocin. Immunoreactive oxytocin was present in the Leydig cells and in the spermatids of the adult and the 263-day bandicoots and there was faint staining in the 123-day bandicoot. Mesotocin was not present in the testes of the bandicoot. Immunoreactive oxytocin and mesotocin were present in the ventral portion of the prostate. The oxytocin within the testis may play a role in spermatogenesis and in seminiferous tubule contractility whereas the hormones present in the accessory glands may have a role in sperm transport in the female reproductive tract.

The response of rat adrenal medulla to oxytocin

Effects of oxytocin (OT) on the adrenal chromaffin tissue of male rats were examined by coupled morphometric and biochemical techniques. Synthetic OT was administered in doses of 0.14 and 0.25 IU/100 g/d during 7 or 10 consecutive days and the effects were followed 1, 24, 72 and 168 hours after the last injection. The function and structure of chromaffin cells were affected by the higher dose of OT only. They caused divergent responses on their amine contents. Adrenaline, noradrenaline and dopamine contents were increased, while serotonin content was decreased. These changes were different in duration and time of incidence. Stereological analysis showed an enhanced number of chromaffin cells and an increase in their total volume. The parallelism between the changes in chromaffin cell number and the catecholamine content strongly suggests a mitogenic effect of the applied OT.

Effect of arginine vasopressin and oxytocin on acetylcholine-stimulation of corticosteroid and catecholamine secretion from the rat adrenal gland perfused in situ

The effects of acetylcholine, arginine vasopressin (AVP) and oxytocin (OXT) on both catecholamine and steroid secretion have been investigated using the isolated rat adrenal gland perfused in situ. Significant stimulation of steroid (aldosterone and corticosterone) secretion occurred with 1 mumol/l acetylcholine; the ED50 was approximately 20-fold higher (circa 20 mumol/l) than that for catecholamine secretion. The highest concentration of acetylcholine used (100 mumol/l) stimulated aldosterone secretion eight-fold; corticosterone secretion four-fold; noradrenaline and adrenaline secretion three-fold. AVP at 100 nmol/l but not at 1 nmol/l significantly stimulated the secretion of both steroids and catecholamines. OXT had no significant effect on corticosteroid or catecholamine secretion at either concentration. The effects on aldosterone secretion of simultaneous administration of acetylcholine and AVP were additive. No similar effect was seen on corticosterone or catecholamine secretion where the degree of stimulation was the same as for acetylcholine alone. OXT (100 nmol/l) inhibited acetylcholine-stimulated aldosterone secretion but had no effect on acetylcholine-stimulated catecholamine secretion. Carbachol was equipotent with acetylcholine in stimulating steroid secretion from the perfused gland. Our results support the hypothesis that acetylcholine may play a role in the control of steroid secretion by the rat adrenal cortex. They fail to support a role for AVP and OXT in modulating catecholamine secretion by the adrenal medulla except at high concentrations.

The effect of oxytocin infusion on adenohypophysial and adrenal cortical responses to insulin-induced hypoglycaemia

The responses of plasma adrenocorticotrophin (ACTH), cortisol, growth hormone (GH) and prolactin to insulin-induced hypoglycaemia were studied in six lean male subjects (age 22-29 years). Intravenous insulin tests were performed with and without oxytocin infusion. Blood sugar nadir occurred at the onset of symptoms (time S) with no significant differences between oxytocin and saline infusion. During the oxytocin infusion mean plasma oxytocin increased from 1.9 pmol/l to 138 pmol/l. Peak increase in plasma ACTH (oxytocin 266 +/- 54 ng/l; saline 281 +/- 43 ng/l, mean +/- SEM) was at S + 10 min while peak plasma cortisol (oxytocin 680 +/- 47 nmol/l: saline 656 +/- 40 nmol/l) was measured at S +/- 60 min, peak GH (oxytocin 96 +/- 17.8 mU/l; saline 106 +/- 18.6 mU/l) at S + 60 min and prolactin (oxytocin 1332 +/- 239 mU/l; saline 1242 +/- 273 mU/l) at S + 30 min. There were no significant differences in plasma concentrations of ACTH, cortisol, GH or prolactin between saline and oxytocin infusion. The results indicate that oxytocin has no effect on plasma ACTH, cortisol, GH and prolactin responses to insulin-induced hypoglycaemia. In particular they fail to support previous studies which suggested an inhibitory role for oxytocin in ACTH secretion.