The beta-adrenoceptor-blocking drug propranolol prevents secretion of immunoreactive beta-endorphin and alpha-melanocyte-stimulating hormone in response to certain stress stimuli

Handled female Wistar rats were exposed to one of the following stress stimuli: restraint, electric foot shocks, passive avoidance situation, ether, or nembutal anesthesia followed by ip formalin or laparotomy. Trunk blood was collected 2-4 min after initiation of the stress stimulus for the determination of immunoreactive beta-endorphin (beta-ENDi), ACTH (ACTHi), and alpha-MSH (alpha-MSHi). All stressors evoked a rapid increase of circulating beta-ENDi to 0.75-2.10 ng/ml. All except passive avoidance situation also induced a rapid increase of plasma ACTHi to 0.45-0.70 ng/ml, whereas plasma alpha-MSHi increased after ether and restraint to 0.18-0.40 ng/ml but was not affected by formalin stress. To study the involvement of a beta-adrenoceptor mechanism in stress-induced peptide secretion, rats were treated with D-propranolol or L-propranolol 40 min before stress exposure. Propranolol did not prevent the increase of plasma ACTHi to any of the stressors studied. L-Propranolol but not its inactive D-isomer reduced (restraint, passive avoidance) or abolished (electric foot shocks) the increase in plasma beta-ENDi but did not affect the beta-ENDi response to other stressors (ether, formalin, laparotomy). Similarly, L-propranolol attenuated the alpha-MSHi response to restraint but not to ether stress. To discriminate between corticotroph or melanotroph origin of beta-ENDi released during stress, rats were treated with dexamethasone or were subjected to neurointermediate lobectomy (4 weeks). Neurointermediate lobectomy did not affect basal or stress-induced plasma ACTHi but resulted in undetectable alpha-MSHi levels. It largely prevented the beta-ENDi response to restraint stress (propranolol sensitive) but had little effect on the beta-ENDi response to formalin stress (propranolol insensitive). Conversely, dexamethasone prevented stress-induced ACTHi response without affecting plasma alpha-MSHi. The beta-ENDi response to restraint stress (propranolol sensitive) was not changed but the response to formalin stress (propranolol insensitive) was largely prevented by dexamethasone. These results show that the intermediate lobe is the main source of beta-ENDi secreted during exposure to stressors with a high emotional impact. Since intermediate lobe peptide secretion induced by such stimuli can be prevented by beta-adrenoceptor blockade, we speculate that stress-induced discharge of catecholamines, possibly from the adrenal medulla, is the trigger signal for peptide secretion from the melanotrophs during this type of stress.

The effect of osmotic challenge and subsequent rehydration on the aging hypothalamo-neurohypophyseal system. A quantitative morphological study of the supraoptic nucleus

The neurons of the supraoptic nucleus (SON) of male C57BL/Icrfat mice at 6 or 28 months of age were examined from normally hydrated, osmotically loaded and osmotically loaded/rehydrated animals. Using quantitative morphological techniques it was shown that the majority of the ultrastructural variables investigated were controlled in the same way in the SON neurons of young and old mice. The major exception was the mitochondrial compartment which although maintaining a constant proportion of the volume of the SON cell did show a significant reduction in the number of mitochondria in the old group, particularly during the osmotic challenge period of the experiment. The "lipid" body compartment of the SON neuron also behaved differently in the cells from the older age group. This study when viewed in conjunction with previous investigations suggests that these SON neuroendocrine neurons from old animals are able to produce hormone until late in the life-span. However, other aspects of cellular activity appeared to be altered when judged by morphological criteria. It is concluded that the SON neurons from these old mice are able to synthesize hormone-containing organelles to the same concentration as the cells from a younger animal. However, the efficiency of the process, or at least the efficiency of concomitant cellular processes, must be questioned in view of the alterations in the rough endoplasmic reticulum, mitochondrial and lysosomal systems.

The role of adrenal medulla and neurohypophysis in the central and peripheral cardiovascular effects of neurohypophysial peptides

The cardiovascular effects of intravenous and intracisternal administration of neurohypophysial peptides were compared in normal, diabetes insipidus and adrenal demedullated chloralose anaesthetized dogs. In normal dogs, intravenous lysine vasopressin (0.1 to 100 mU/kg) induced a dose-dependent increase in blood pressure with bradycardia whereas intracisternal injection (0.01 to 10 mU/kg) elicited a dose-related decrease in blood pressure but no change in heart rate. Intracisternally injected oxytocin (1 and 10 mU/kg) increased blood pressure. The central hypotensive effects of vasopressin were not observed in diabetes insipidus or adrenal demedullated dogs. In contrast, the central pressor properties of oxytocin were still observed in these two groups of animals. These results show that the central cardiovascular properties of vasopressin (but not those of oxytocin) may vary according to the hormonal state of the animals. Intracisternal vasopressin induces an hypotensive response due to a decrease in sympathetic tone and dependent on the integrity of the neurohypophysial tractus.

Decreased corticotropin-releasing factor-like immunoreactivity in rat intermediate and posterior pituitary after stalk section

We determined the corticotropin-releasing factor(CRF)-like immunoreactivity by radioimmunoassay in intermediate and posterior pituitary lobes of stalk-sectioned and sham-operated control rats. The antigenic determinant read by the CRF antibody used was contained within the region of amino acids 26 (Gln) to 37 (Leu) of the molecule. Intermediate and posterior lobes of control rats contained similar amounts of CRF (591 +/- 78 and 487 +/- 34 pg/mg protein, respectively). The section of the pituitary stalk produced a marked decrease in CRF-like immunoreactivity in both structures. The CRF content on the intermediate lobe after stalk section was 62 +/- 17 pg/mg protein, a decrease of 90%, and that of the posterior lobe was 90 +/- 13 pg/mg protein, an 83% decrease. Our results suggest that most of the CRF-like immunoreactivity in the rat intermediate and posterior pituitary lobes is contained in nerve fibers of brain origin and support the hypothesis of a role of CRF in the release of intermediate and posterior lobe peptides.

Effect of cooling on supraoptic neurohypophysial neuronal activity and on urine flow in the rat

The activity of antidromically identified supraoptic neurosecretory neurones was recorded in Sprague-Dawley rats under urethane or sodium pentobarbitone anaesthesia during cooling of the body with a cold pack. Of twelve phasic neurones studied during a complete cooling and rewarming cycle, six displayed an initial increase, followed by a depression in activity during the period of reduced body temperature. The remaining six phasic neurones did not alter their activity during cooling. Non-phasic neurohypophysial neurones displayed a reversible reduction (n = 8), or increase (n = 6) in activity during cooling, while seven neurones were unaffected by changes in body temperature. In four other anaesthetized Sprague-Dawley rats, urine flow was reduced by approximately 50% during cooling; this was followed by a diuresis after removal of the cold pack and return of body temperature to normal. The antidiuresis did not occur in homozygous Brattleboro rats which lack arginine vasopressin. The electrophysiological data from a proportion of the supraoptic neurohypophysial neurones correlate with the observed changes in urine flow.

Reproducible increases in intramammary pressure after spinal cord stimulation in lactating rats

Intramammary pressure was recorded in anaesthetized lactating rats during electrical stimulation of the anterolateral pathways in the T12/L1 region of the spinal cord. In 18 rats, electrical stimulation at 10 Hz or more for 10-30 s caused a reproducible increase in intramammary pressure. The mammary gland responses were similar to those resulting from stimulation of the neurohypophysis with the same parameters, and were eliminated after complete destruction of the neural stalk; they were not associated with any consistent change in blood pressure. In 3 rats, a mammary gland response to spinal cord stimulation was obtained only after administration of the beta-adrenergic blocker, propranolol, which facilitates suckling-induced reflex milk-ejections. These results suggest that spinal cord stimulation can cause the release of oxytocin; the functional significance of such a release is discussed in relation to the milk-ejection reflex.

Connections of hypothalamic paraventricular neurons with the dorsal medial thalamus and neurohypophysis: an electrophysiological study in the rat

Connections between the hypothalamic paraventricular nucleus (PVN) and thalmic paraventricular nucleus ( PVT ) were examined using electrophysiological methods. Efferent projections of adjacent PVN cells were defined on the basis of antidromic activation from either PVT (n = 12) or neurohypophyseal (n = 38) stimulation; antidromic activation from both sites (n = 3) suggested that some PVN cells project both to the PVT and to the neurohypophysis. PVT stimulation evoked only weak orthodromic responses from 21% of PVN neurohypophyseal neurons, whereas short latency, high probability orthodromic responses were observed from 43% of PVN non-neurosecretory neurons. These data indicate reciprocal PVN- PVT connections and suggest that PVT afferents preferentially innervate non-neurosecretory PVN cells.

In vivo biosynthesis and transport of oxytocin, vasopressin, and neurophysins to posterior pituitary and nucleus of the solitary tract

A growing body of literature suggests that oxytocin (OXY) and arginine-vasopressin (AVP), in addition to their neuroendocrine roles, may serve as neuromodulators within the central nervous system of mammals. The present study investigated the biosynthesis of OXY, AVP, and their associated neurophysins in the paraventricular nucleus of the hypothalamus (PVN) and the transport of these peptides to the neural lobe and the nucleus of the solitary tract (NTS) in the brainstem of the rat. Rats were cannulated bilaterally in the PVN, and 24 hr later a 2-hr pulse of [35S]cysteine was administered using an Alzet minipump delivery system. After a 10-hr chase period, the neural lobe was removed and the PVN and NTS were punched. Tissue homogenates were adsorbed to and eluted from octadecyl-silica cartridges and analyzed by linear high performance liquid chromatography (HPLC) gradient elution, chemical and enzymatic modification, and exponential gradient HPLC elution followed by linear HPLC gradient analysis using an ion-pairing buffer system. This rigorous approach has allowed us to identify 35S-labeled material which co-purifies with OXY and AVP from the PVN, neural lobe, and NTS samples. Specific transport of the nonapeptides to the NTS was demonstrated when a unilateral transection of the hypothalamic fibers resulted in a unilateral depletion of the radiolabeled peptides from the NTS samples. Additionally, each of the neurophysins was purified from the neural lobe and NTS samples after linear HPLC gradient analysis, ion-pairing buffer linear gradient analysis, then tryptic digestion followed by exponential gradient HPLC analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Posterior pituitary involvement in the control of luteinizing hormone and prolactin secretion during the estrous cycle

The effects of removal of the posterior lobe of the pituitary on plasma concentrations of PRL, LH, and FSH were examined under the following conditions: on each morning of the 4-day estrous cycle, 2 weeks after ovariectomy, and 2 h after the administration of a LHRH inhibitory analog on estrus. Blood was collected from a femoral artery immediately before and during the 3 h after posterior pituitary lobectomy or sham lobectomy. Significant elevations of both PRL and LH were seen after removal of the posterior pituitary on estrus and diestrus day 1, while no change was seen in the plasma concentration of either hormone after posterior pituitary removal on diestrus day 2. On proestrus, posterior lobectomy resulted in an elevation of LH only. The posterior lobectomy-induced PRL elevations were rapid and of short duration, while those of LH were delayed and prolonged. No alteration in plasma FSH concentrations was seen after posterior pituitary lobectomy performed on any day of the estrous cycle. In contrast to the hormonal elevations observed after lobectomy during the cycle, no change in plasma PRL, LH, or FSH was seen after posterior lobectomy in ovariectomized rats. The administration of a LHRH inhibitory analog 2 h before posterior lobectomy completely abolished the lobectomy-induced rise of LH normally seen on estrus. The data suggest that the posterior pituitary participates in the regulation of PRL and LH, but not FSH, release during the estrous cycle. Given that the posterior lobectomy-induced elevations of plasma PRL and LH were evident only on certain days of the cycle and were absent in ovariectomized rats, it is likely that posterior pituitary inhibition of PRL and LH release is expressed only in the presence of specific ovarian hormonal profiles. In addition, the posterior lobectomy-induced rise in plasma LH appears to be dependent on the presence of LHRH, but it remains to be determined whether a posterior pituitary substance(s) alters hypothalamic release of or anterior pituitary responsiveness to LHRH.

Effect of dexamethasone on immunoreactive corticotropin-releasing factor in the rat median eminence and intermediate-posterior pituitary

Immunoreactive ACTH (I-ACTH) concentrations in the anterior pituitary, intermediate-posterior pituitary (IP), and plasma and immunoreactive corticotropin-releasing factor (I-CRF) concentrations in the median eminence and IP were determined in rats receiving dexamethasone for various periods from 16 h to 10 days. Plasma I-ACTH concentrations were decreased 16 h after a single injection of dexamethasone. Anterior pituitary I-ACTH concentrations did not decrease until 4 days after the start of dexamethasone medication. IP I-ACTH concentrations did not change throughout these periods. I-CRF concentrations in median eminence and IP rapidly decreased after dexamethasone administration. These results raise the possibility that the source of I-CRF in the IP is hypothalamic.

[Projections of the visceral and somatic afferent systems to identified neurons of the supraoptic nucleus]

Antidromic identification of the hypothalamic supraoptic nucleus' neurosecretory cells in cats in the course of stimulation of the posterior hypophysis aided to study the possibility and degree of modulation of the unit activity by ascending visceral and somatic afferent signals during stimulation of the splanchnic and sciatic nerves. the data obtained revealed that the major part of the neurosecretory neurons cannot be activated by means of the afferent signals. The projections of visceral and somatic afferent systems represented by the splanchnic and sciatic nerves, spread over to the nonroendocrinal cells of the hypothalamic supraoptic nucleus. The functional role of peripheral afferents in modulation of the hypothalamic neuroendocrinal neurons activity, is discussed.

The response of plasma arginine vasopressin to 14 h water deprivation in the elderly

The response of plasma arginine vasopressin (AVP) to 14 h water deprivation was investigated in 30 healthy elderly individuals ranging in age from 63 to 87 years, with a mean age of 76.5 years. The mean AVP concentrations, both at normal hydration and after the water deprivation test, were significantly lower than those in the young. Moreover, the post-test mean value of Uosm/Posm in the elderly increased up to 1.55 +/- 0.52, which is lower than that in the young in whom the value was greater than 2. These results suggest that the aged are prone to incomplete diabetes insipidus. This pathological state might predispose to electrolyte imbalance in the elderly.

Influence of vasopressin and angiotensin on baroreflexes in the dog

Cardiovascular responses to step-changes of carotid sinus pressure were evaluated at normal and elevated levels of plasma arginine vasopressin in anesthetized neurohypophysectomized dogs (n = 12). Arginine vasopressin influenced autonomic function in two ways: first, maximum carotid reflex gain increased; second, cardiac output was decreased. The enhancement of reflex strength was observed only in response to decreases of intrasinus pressure below the equilibrium point (pressures of between 60 and 105 mm Hg). Aortic pressure rose twice as high for a given decrease of intrasinus pressure, elevations of total peripheral resistance responses were triple those observed at normal plasma arginine vasopressin. In this way, arginine vasopressin more than doubled the ability of the carotid reflexes to return a drop in arterial pressure to normal. Arginine vasopressin enhancement of reflex gain was not observed with elevations of intrasinus pressures above the equilibrium point. Elevation of aortic pressure expected from the vasoconstrictor actions of infused arginine vasopressin were buffered by associated reductions in cardiac output. Vagally mediated bradycardia was consistently observed with elevated arginine vasopressin, but the reflex response of heart rate to step-changes of intrasinus pressure was unchanged. Time control studies in five neurohypophysectomized dogs indicated no significant change in carotid reflex response over the 3- to 4-hour protocol. Comparison of reflex responses in anephric dogs (n = 8) at low and elevated levels of angiotensin II indicated that this vasoactive peptide did not significantly alter reflex responsiveness. We conclude that arginine vasopressin enhances the ability of the carotid reflexes to normalize decreases of arterial pressure, but buffers a rise in pressure from its own vasoactive properties by initiating a fall of cardiac output.

Dynamic neuronal-glial interactions in hypothalamus and pituitary: implications for control of hormone synthesis and release

Various lines of evidence have suggested that astrocytes play a dynamic role in control of hormone synthesis and release from the CNS. The model system most studied has been the rat hypothalamo-neurohypophysial system, consisting chiefly of the supraoptic and paraventricular nuclei and their axonal terminals. Neurons of this system manufacture and secrete oxytocin and vasopressin. Electron microscopic studies have shown that certain physiological conditions (e.g., dehydration, lactation) produce increases in direct apposition among these neurosecretory cells, an effect due to withdrawal of glial processes from between the neurons. Neurohypophysial astrocytes (pituicytes) show dynamic interactions with the neurons at the level of the terminals, by engulfing them and interposing processes between the terminals and the basement membrane when hormone demand is low. Pituicyte processes retract from both areas when hormone demand is high, allowing the neuronal terminals direct access to the perivascular space. Recently, osmotic manipulations (in the physiological range) have shown that these changes can be produced in vitro in neurohypophysial explants without stimulated hormone release. Experiments on cultured adult rat pituicytes have revealed similar morphological changes in response to noradrenaline. These changes were reversed or blocked by propranolol. The increase in direct soma-somatic apposition (7-9 nm separation) of magnocellular neurons could produce a tonic rise in (K+)o which would increase protein synthesis and contribute to the raised excitability of these neurons. Also, the removal of interposed glia could allow the formation of gap junctions and specialised synapses which are known to occur between these neurons. These in turn may participate in producing the coordinated firing that maximizes hormone release. The interactions of pituicytes with the terminals in the neurohypophysis suggests that these astrocytes are also a part of the mechanism of control of hormone release.

In vitro and in vivo studies on development and regeneration of vasopressin neurons

The present paper reviews recent work conducted in our laboratory on vasopressin neurons either grown in culture or transplanted into vasopressin deficient rats. The in vitro model of reaggregated cell culture used the anterior hypothalamus, including vasopressin neurons of the SON from normal timed-pregnant LE rats of similar ages used in our in vivo model. Various cells were co-cultured with their known target tissue, the posterior pituitary to analyze further the influence of the target tissue on hormone production. At a designated end point, cultured cells were fixed and stained immunocytochemically for vasopressin and neurophysin. Radioimmunoassay of the samples was performed for vasopressin quantification. Hypothalamic cells from all ages produced vasopressin (VP). The co-culturing of hypothalamus with posterior pituitary produced a significant increase in VP. Correlative transplantation studies were conducted using timed-pregnant Long-Evans (LE) rats at various days post coitus (dpc) and neonatal tissue from 0- and 5-day old rat pups. Animals survived about 40 days then were perfused and their brains processed for vasopressin and neurophysin thick-section immunocytochemistry. The results showed that the capability for survival of younger grafts was much greater than that of older tissue. With this paper, we have shown that the reaggregation of anterior hypothalamic cells in a culture system can be used for microassay of neurosecretory activity. These data suggest a close correlation between the ability of a neuron to survive transplantation and its stage of development. With the present studies, we have shown that neurons not fully differentiated maintain a greater degree of plasticity than older tissue and are better able to survive the rigors of transplantation and that various manipulations of environmental factors have an effect on brain development at critical times.

Method for quantitating the molecular content of a subcellular organelle: hormone and neurophysin content of newly formed and aged neurosecretory granules

A method is described for the quantitative determination of the content of subcellular organelles such as secretory granules. Purified subcellular fractions of the organelle are prepared and aliquots are assayed for hormones, for example. To determine the number of organelles per fraction, known numbers of latex particles of a size similar to the organelle are added to other aliquots of the subcellular fractions. Latex particles and organelles are then pelleted together by centrifugation. The ratio between latex particles and organelles can be determined by morphometric analysis of ultrathin sections taken through the full thickness of the pellet. The number of organelles and hence their content of the substance assayed can then be calculated. We have applied this technique to posterior pituitary neurosecretory granules, the content of which has already been estimated by a different method. Newly formed neurosecretory granules from oxen and rats were found to have a content of approximately equal to 85,000 molecules of hormone and neurophysin. Aged neurosecretory granules from the same neural lobes appeared to contain less hormone and neurophysin, but this was shown to be the result of loss of material from the granules during isolation in media of 360 mosM. Such loss could be prevented by isolation in hypertonic (660 mosM) media.

Actions of neurohypophysial peptides on pancreatic hormone release

The intermittent reports concerning metabolic actions of neurohypophysial extracts or hormones encouraged us to study the effect of these substances on the function of the endocrine pancreas. A surprisingly small amount of neural lobe (NL) extract (0.025 NL eq/ml) stimulated a 425% increase in the release of glucagon from islets isolated from the pancreas of the rat. Gel filtration of the extract produced an elution profile of glucagon-releasing activity that was superimposable on the profiles of oxytocin (OT) and arginine vasopressin (AVP). Synthetic OT and AVP each elicited a concentration-dependent stimulation of glucagon release but failed to influence insulin release in medium 199 containing 5.6 mM glucose. They were effective at 0.2 ng/ml (+55%, +50%) and produced a striking increase (five- to sevenfold) at 20 ng/ml. The response to each peptide was greatly diminished in the presence of a higher concentration of glucose (11 mM). The lysine, desamino-, and 1,6-aminosuberyl analogues of vasopressin, vasotocin, and AVP are equipotent peptides, whereas the desglycinamide analogue, pressinoic acid, and angiotensin II were inactive. Injection of AVP (1 microgram iv) produced a rapid increase in peripheral glucagon (+185% in 5 min). The response to injection of OT was less rapid (+105% in 15 min), but in each case elevation of insulin was also observed. Our results provide evidence that OT and AVP can act directly on the endocrine pancreas and may help explain previous reports of metabolic actions of these peptides.

Oxytocin release is inhibited by opiates from the neural lobe, not those from the intermediate lobe

Previous experiments have shown that the amount of oxytocin released by electrical stimulation from an isolated rat neurointermediate lobe is about doubled in the presence of the opiate antagonist naloxone. To test whether the opiates from the intermediate lobe inhibit the release of oxytocin, we performed similar experiments on the isolated neural lobe, after almost total removal of intermediate lobe tissue. The potentiating effect of naloxone upon oxytocin release was undiminished, suggesting that the endogenous opiate responsible for inhibiting oxytocin secretion comes from the neural lobe itself.

Microheterogeneous neurophysins in newly formed and aged neurosecretory granules

To find out, whether microheterogeneity of neurophysins is due to aging of neurosecretory granules we investigated neurophysin proteins of porcine origin from newly formed and aged granules, as well as from two different extraction methods from whole posterior pituitary glands by high performance liquid chromatography. In newly formed as well as in aged granules all microheterogeneous forms of the neurophysins were present in nearly identical relation suggesting that microheterogeneity is not due to maturation or post matural degradation. In comparison, the crude material obtained by the method of Uttenthal and Hope showed a comparable content of the different neurophysins while Chauvet's method resulted in a different HPLC pattern. In summary, neurophysin heterogeneity is obviously not due to aging processes.

Release of oxytocin into blood and cerebrospinal fluid by electrical stimulation of the hypothalamus or neural lobe in the rat

Oxytocin (OT) was measured in blood and cerebrospinal fluid (CSF) samples obtained from anaesthetized rats. Release of OT was evoked by electrical stimulation (15 s) of the hypothalamus or the neural lobe. Stimulation of the neural lobe increased plasma OT sevenfold without altering CSF levels. Hypothalamic stimulation released OT into both blood and CSF, although the rise in CSF was both delayed and prolonged compared to that in plasma. Stimulation sites which released OT into CSF extended over a large medial area of the hypothalamus. More lateral stimulation sites were much less effective. Our results show that the release of OT into blood and CSF can be dissociated and that CSF levels reflect the activity of those hypothalamic OT-neurones which do not project to the neural lobe.

Optical recording of action potentials from vertebrate nerve terminals using potentiometric probes provides evidence for sodium and calcium components

Optical methods are shown to monitor action potentials from a population of nerve terminals in the neurohypophysis of Xenopus. Calcium antagonists such as cadmium and nickel ions block a component of the action potential that probably reflects a calcium-mediated potassium conductance, and tetrodotoxin blocks an inward sodium current, revealing a calcium component to the action potential upstroke.

Brain opiates and neuroendocrine function

Opioid peptides are found throughout the central nervous system, and have profound effects on neuroendocrine function. In man, exogenous opiates and opioids elevate circulating prolactin, GH and TSH, and suppress the release of the gonadotrophins and pro-opiocortin-related peptides. However, unlike in other species, there is substantial evidence for a physiological role of endogenous opioids only in the case of the gonadotrophins and ACTH/LPH. Most evidence suggests that LH and FSH are modulated via the hypothalamus or amygdala, where concentrations of opioids and opioid receptors are very high. Endogenous opioids appear to be principally concerned with the frequency-modulated release of GnRH, and this may be important clinically in patients presenting with amenorrhoea. ACTH/LPH are under tonic inhibition by endogenous opioids acting at hypothalamic and/or pituitary levels, and changes in this inhibition may be responsible for the release of these peptides in response to certain forms of stress. It has been reported that the opiate antagonist, naloxone, is clinically useful in paradoxically inhibiting the release of ACTH in patients with Nelson's syndrome, but this requires adequate confirmation. Vasopressin is under biphasic opiate control, but the principal effect is probably opiate-mediated inhibition of vasopressin release. The endogenous ligand for this response is likely to be dynorphin. Suppression of vasopressin release by opiates may become a useful therapy in the treatment of the 'Syndrome of inappropriate ADH'.

A multigene family for the vasopressin-like hormones? Identification of mesotocin, lysipressin and phenypressin in Australian macropods

Mesotocin ([Ile8]-oxytocin), lysipressin ([ Lys8]-vasopressin) and phenypressin ([Phe8]-vasopressin) have been identified in the western gray kangaroo (Macropus fuliginosus) as well as four other macropodids. Lysipressin and phenypressin, which differ by the amino acids in positions 2 (Tyr/Phe) and 8 (Lys/Arg) are likely products of two separate vasopressin-like genes. It is assumed that arginine vasopressin found in most mammals is the product of two identical genes which can be revealed in some species by differential mutations as seen usually in marsupials. The duality can also be revealed by differential mutations in another domain of the precursors, such as the neurophysin (MSEL-neurophysin), as observed in the ox.

Maternal-fetal neurohypophyseal system

The author reviews our present understanding of neurohypophyseal peptide metabolism and physiology, an understanding that is largely based upon the isolation and accurate measurement of arginine vasopressin, oxytocin, and arginine vasotocin. Discussed are both the major advances in understanding and the areas of inquiry that remain or that have been newly opened.