The dynamics of beta-endorphin release by the hypothalamic nuclei and pituitary gland in sheep under physiological and stress condition

The secretion of beta-endorphin (beta-End) by the infundibular nuclei--median eminence (IN-ME) and paraventricular nuclei (PVN) of the hypothalamus and the anterior lobe (AL) of the pituitary gland was determined in 18 anestrous ewes by RIA assay of this opioid in perfusates collected from these formations. Perfusion with Ringer-Locke solution was carried out on the animals under resting and stress-full conditions, using a pushpull cannula method. Electrical footshocks were used as stress stimuli. Two series of perfusion experiments were performed. In the first, the perfusions were carried out over two hours and perfusates were collected before and during stress for 1 h. In the second series of experiments the dynamics of the release of the opioid by the IN-ME and the pituitary gland were followed by collecting five or six perfusates in 20 min fractions before and during stress, respectively. The first series of experiments showed that the concentrations of beta-End in perfusates from the pituitary gland were much higher than those from the hypothalamic nuclei and that the concentrations of this opioid during stressing rose significantly only in perfusates from the IN-ME nuclei. In the second series of experiments the release of beta-End from the IN-ME and pituitary gland was altered by stress. The shift was very characteristic in that the concentrations of the opioid during stimulation initially significantly rose and then gradually declined. The concentration of the opioid in the peripheral blood also rose at the beginning of stimulation and declined as stimulation continued.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancing effect of intracerebrally infused beta-endorphin antiserum on the secretion of cortisol in foot-shocked sheep

It was found in our earlier experiments that infusion of beta-endorphin (beta-End) into the 3rd brain ventricle in sheep elicited a differential effect on the secretion of cortisol under physiological and stress conditions. Under physiological conditions it elevated the level of cortisol in the peripheral blood, while in stressed animals it suppressed it. To obtain further support for the suppressive action of beta-End on cortisol secretion under stress conditions a beta-End antiserum was infused into the 3rd ventricle of the brain in stressed and nonstressed sheep and the concentration of plasma cortisol was measured. Stress was induced by mild electric foot shock. Infusion of the beta-End antiserum during stimulation enhanced the plasma cortisol values, when compared with those obtained during the infusion of rabbit hyperimmune serum containing anti-guinea pig gamma-globulins or saline. Moreover, during the infusion of beta-End anti-serum some aggravation of stress symptoms expressed by the increase of restlessness and higher frequency of defecations and urinations was observed. Additional experiments carried out to study the effect of beta-End on prolactin (PRL) secretion showed that this opioid induced a very high secretion of PRL in stressed animals. On the basis of these data and the known suppressive action of PRL on the corticosterone response to stress in the rat, we suggest that the suppressive action of beta-End on cortisol secretion in stressed sheep could be caused by the action of PRL.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of luteinizing hormone-releasing hormone, beta-endorphin and noradrenaline by the nucleus infundibularis/median eminence during periovulatory period in the sheep

The relationships between the release of LHRH, beta-endorphin (beta-END) and noradrenaline (NA) from the hypothalamic infundibular nuclei/median eminence (NI/ME) during the periovulatory period in the ewe was studied. Neurohormone release was assayed in perfusates collected from the NI/ME via push-pull cannulae. LHRH concentrations in perfusates ranged from below detectable values (5 pg) to 50 pg and from 15 to 240 pg/20 min perfusate on the days of proestrus and estrus, respectively. beta-END concentrations in perfusates ranged from 320 to 6,000 pg on the day of proestrus and fell to a range between 100 and 380 pg/20 min perfusate on the day of estrus. The NA content of perfusates ranged from an undetectable level to 0.9 x 10(4) pg/perfusate during proestrus, and rose from 1.0 x 10(4) to 6.6 x 10(4) pg/perfusate shortly before the preovulatory release of LHRH and LH. On the basis of the present observations, the following sequence of events leading to the massive LH ovulatory surge in the sheep is suggested: (1) increased secretion of beta-END in the NI/ME on the day of proestrus generates an increase in the releasable pool of LHRH through inhibition of LHRH release; (2) on the day of estrus a decreased release of beta-END allows the expression of NA activity in the NI/ME and the augmentation of NA tone facilitates the release of newly accumulated LHRH; (3) the resultant intensified LHRH output with its significantly changing pattern of release triggers the preovulatory surge of LH.

Suppressive effect of beta-endorphin and naloxone on the secretion of cortisol under stress conditions in sheep

The effect of an infusion of beta-endorphin and naloxone into the 3rd cerebral ventricle on the blood serum concentration of cortisol in non-stressed and stressed anoestrous sheep was studied. The infusion of naloxone alone did not alter the secretion of cortisol in non-stressed animals but the response to footshock was inhibited in that the cortisol values were significantly lower (P less than 0.05) when compared with those during the infusion of saline and footshocking. This opiate antagonist also suppressed the cortisol response to an infusion of beta-endorphin (P less than 0.001 and P less than 0.05). When the sheep infused with beta-endorphin were additionally exposed to footshock there was less enhancement of the secretion of cortisol (P less than 0.001 and P less than 0.05). The depressive action of beta-endorphin upon cortisol secretion in stressed sheep is matched by corresponding observations on man and it seems that endogenous opioids may inhibit or attenuate some hormonal responses to stress.

Effect of stress on the course of oestrous cycle and the release of luteinizing hormone; the role of endorphin in these processes

It has been postulated that stress induces discorrelations of the hypothalamo-pituitary and pituitary gonadal axis. In our experiments on the effect of stress on the reproductive physiology in rats and sheep we applied mild electrical footshocking of short or prolonged duration. Foot-shocking applied with some breaks during 9 h within one a day (15th day of the oestrous cycle) induced in ewes acceleration of the release of LH. Prolonged footshocking applied with some breaks during 3 days in cycling sheep caused disturbances in the circadian rhythm of the cortisol secretion, disturbances in the release of LH and led to the blockade of ovulation. Disturbances in the course of oestrous cycle occurred not only during the current cycle but also during two subsequent cycles. Rats exposed to relatively long-term stressful situation (24 h) during dioestrous displayed marked changes in the length of this phase in three subsequent post-stress oestrous cycles. To follow the neurohormonal background of the stress-induced disturbances in LH release and in the course of oestrous cycle in sheep the concentrations of beta-endorphin (beta-END) in the infundibular and paraventricular nuclei as well as in the pituitary gland under physiological and stress conditions were determined, while in rats the metabolism of brain serotonin was investigated. Footshocking in rats induced significant decrease in 5-HT concentrations in the fronto-parietal brain cortex, hippocampus, striatum, medial basal hypothalamus and the preoptic-anterior hypothalamic area. These results allow to suggest that the decline in brain 5-HT under stress conditions has some associations with the impairments in the course of oestrous cycle. Measurements of the beta-END in perfusates of medial basal hypothalamus (nucl. infundibularis) in sheep evidenced significant increase of this opioid under stress conditions and it was postulated that this increase might be the main cause of the stress-induced impairments in the course of oestrous cycle and inhibition of LH-release. In addition, it was found that beta-END suppressed the secretion of cortisol and attenuated some noxious consequences of general nature for organism.

Differential behavioural and hormonal responses to two different stressors (footshocking and immobilization) in sheep

Two different stressors footshocking and immobilization applied for 3 days induced in sheep differential behavioural and hormonal responses in cortisol and prolactin secretion. Immobilization drastically disturbed rumen motoric activity (significantly attenuated its contractions), caused loss of appetite and severe general depression. Footshocking did not induce any of these symptoms. Immobilization induced 2-3 fold higher rise of plasma cortisol mesors on the days of stressing as compared to footshocking. On the poststressing days after footshocking as well as after immobilization plasma cortisol mesors fell to 50% of the prestimulatory values. The rise of plasma prolactin mesors in footshocked and in immobilized animals on the days of stressing was nearly of the same magnitude. However, a significant difference in the response of prolactin secretion between footshocked and immobilized animals occurred in the circadian rhythmicity of the hormone secretion. Footshocking induced circadian rhythmicity with characteristic acrophases, while immobilization did not induce the circadian pattern of prolactin secretion. An attempt of interpretation of the described phenomena has been undertaken.

The effect of 6-hydroxydopamine infusion into the third cerebral ventricle on the plasma prolactin levels in anoestrous ewes subjected to prolonged and repeated stress

The effect of 6-hydroxydopamine (6-OHDA) infusion into the third cerebral ventricle on the secretion pattern of prolactin in anoestrous sheep, subjected to repeated and prolonged stress-stimuli was followed. On the 12-15 th day after the infusion of 6-OHDA into the third cerebral ventricle and after having tested the effect of this infusion on plasma prolactin concentration, the animals were subjected to mild electric footshocks 9 hrs daily (9 a.m.-6 p.m.) for 3 consecutive days. Infusion of 6-OHDA induced a very high rise of plasma prolactin values by about 3 times as compared to those found before infusion (from 118.2 +/- 39.5 to 338.9 +/- 81.7 ng/ml mesor 24 h). On the other hand, the response of the animals pretreated with 6-OHDA to electric stimulation was characterized by the lack of changes in plasma prolactin concentration; their plasma hormone concentrations were neither raised during stimulation nor decreased after the stimulation and were maintained during all these days nearly at the same level as after the infusion of 6-OHDA. Central mechanisms which could account for the so high and prolonged elevation of plasma prolactin concentration after the infusion of 6-OHDA and for the lack of its rise under conditions of prolonged stress are discussed.

Effect of repeated and prolonged stress stimuli on the plasma prolactin concentration in sheep

The effect of repeated and prolonged stress-stimuli applied during 3 days on the plasma prolactin concentration in sheep, in anoestrous, prooestrous and pregnant animals were studied. The following results were obtained: Repeated and prolonged weak electric stimuli applied in the form of footshocks in sheep during 3 days elicited a rise of mesor plasma concentration. The magnitude and the onset of this rise was not associated and dependent on the physiological state of animals. The mesor values of plasma prolactin concentration in all groups of animals except prooestrous ewes on the day following stimulation returned to their prestressing levels. Repeated and prolonged stimuli disturbed circadian rhythm of prolactin secretion existing only in prooestrous ewes, i.e. they caused its disappearance on the days during stimulation and its reappearance on the day following stimulation but at an accelerated and inverse time of the day to that found before stimulation. The induced rise of plasma prolactin concentration in anoestrous and pregnant ewes on the days during electric stimulation showed, according to Cosinor analysis, all features characteristic for acrophase of the circadian rhythm. This phenomenon may be considered as induced acrophase in stress condition.

Changes in circadian rhythm and suppression of the plasma cortisol level after prolonged stress in the sheep

Diurnal variations in the plasma cortisol level were studied in anoestrous, pro-oestrous and pregnant ewes subjected to weak electric stimulation of the fore-limbs 9 h daily for 3 consecutive days. In non-pregnant ewes the cortisol level rose on each of the 3 days when the stimulation was applied and then decreased on the day following the stimulation. A similar decrease in plasma cortisol concentrations in pregnant ewes appeared on the second day of footshocking. The acrophase of the circadian rhythm on electrostimulation days was synchronous with the time of application of footshocks; therefore, in stimulated ewes it was significantly accelerated compared to the prestimulatory day. A decrease in the plasma cortisol level in pro-oestrous and pregnant ewes was accompanied by disappearance of its normal rhythmicity. Since a normal plasma cortisol response to exogenous corticotrophin was noted after 3 days of footshocking it seems unlikely that the decrease in the cortisol level after prolonged stress was caused by exhaustion of the adrenal cortex. Some central mechanisms which could account for the biphasic changes in the plasma cortisol level and for disturbances of the hormone diurnal rhythmicity under conditions of prolonged stress are discussed.

The effect of 6-hydroxydopamine infused into the third cerebral ventricle on the plasma cortisol concentration in sheep subjected to repeated and prolonged stress stimuli

It has previously been observed that sheep subjected to repeated and prolonged stress stimuli showed biphasic cortisol responses. On the first and second day of stimulation an elevation was observed, while on the subsequent days and on the day after the stimulation a marked suppression of plasma cortisol level and a disappearance of its circadian rhythm was noted. It was hypothesized that these changes in the secretion of the hormone were caused by the alteration of catecholaminergic systems in the CNS. To verify this suggestion chemical lesions of the catecholergic systems of the diencephalon were carried out by the infusion of 6-hydroxydopamine (6-OHDA) into the third cerebral ventricle and animals treated in this fashion were subjected to repeated and prolonged electrical mild footshocking (applied during 3 days). The pretreated animals lost the circadian rhythm in cortisol secretion on the days before as well as during and after the electrical stimulation. The animals pretreated with 6-OHDA showed a significant rise of the plasma cortisol level during stimulation. This rise, as the highest daily concentration, occurring within about 1 h after the beginning of footshocking, was significantly accelerated in time with respect to the physiological acrophase, occurring in the early morning hours at the end of prestimulatory days. On the other hand, the pretreated animals did not show the decrease of plasma cortisol levels on the day after the stimulation, observed in normal non-pretreated ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the medial-basal hypothalamus in the secretion of growth hormone during pregnancy and lactation in ewes

The main aim of this study was to examine the role of the hypothalamus in controlling the secretion of GH in the ewe. This was evaluated by studying the effect of lesions placed either in the anterior or the posterior medial-basal hypothalamus (MBH) on the concentration of GH in the peripheral circulation during pregnancy and lactation, i.e. when the levels would be high in normal ewes. Simultaneously, the level of prolactin in the peripheral blood of these animals were followed. Lesions of the MBH resulted in a marked decreasing in circulating GH as well as disturbances in the mammogenic and lactogenic processes during the periods of periparturition and lactation respectively. The changes were particularly evident if the anterior MBH was lesioned. The present experiments confirm our previous findings that a stimulatory centre is localized in the anterior MBH of sheep whilst in the caudal MBH there is an inhibitory centre regulating the release of prolactin. The results also confirm the important role of GH during lactation in ewes, especially during lactogenesis. The results indicate a differentiated but synchronizing and synergistic role of the MBH regulating the patterns of GH and prolactin secretion in late pregnancy and lactation.

The effect of dopamine on the release of prolactin in sheep with lesions of the hypothetical centre producing prolactin inhibiting factor (PIF)

It has been demonstrated in our previous papers that in the anterior part of medial basal hypothalamus (AM BH) in sheep a stimulating, while in the caudal part of MBH (CMBH) an inhibiting centre of prolactin release are situated. These results suggested that CMBH might be the site of PIF production and prompted us to investigate the effect of dopamine (DA) on the concentration of prolactin in the peripheral blood (p.bl.) in animals in which CMBH had been previously lesioned and this concentration was very high. Microinfusion of L-dopamine into the third cerebral ventricle (c.v.) or into the internal maxillary artery in intact as well as in lesioned lactating ewes depressed distinctly the prolactin level in the p.bl. This action of DA suggests that in the CMBH exists dopaminergic system which itself plays an inhibitory role in the control of prolactin release without involvement of PIF.

Immunocytochemistry of luteinizing hormone releasing hormone (LHRH) in the sheep hypothalamus during variuos reproductive stages: correlation with the gonadotropic hormones of the pituitary

Using the labeled and unlabeled immunoperoxidase metods, the distribution and concentration (1) of immunoreactive LFRH-material in the hypothalamus, and (2) of gonadotropic hormones in the adenohypophysis of the ewe were determined during various reproductive stages, including two phases of the estrous cycle, anestrus, lactation, and the state after ovariectomy. The concentration of LHRH-immunoreactive material varied in particular regions of the median eminence (ME) and was closely dependent on the physiological state. The immunoreactive material was most abundant in hypothalami of lactating animals, exceeding gradually the corresponding deposits in ovariectomized animals, in ewes during the 16th day of the estrous cycle (before ovulation), and in anestrous ewes. A severe depletion of LHRH from the rostral and central parts of the ME was observed 24 h after ovulation. This depletion was accompanied by a degranulation of LH- and prolactin-producing cells in the adenophypophysis. It is postulated that LHRH is stored in the ME of the sheep in all examined endocrine stage. Only circumscribed regions of the ME take part in the cyclic release of LHRH during the ovulatory phase; this suggests a functional differentiation of the nerve terminals in this neurohemal area.

Serotonin content of the anterior and medial-basal hypothalamus in the female rats throughout the course of estrous cycle

Serotonin content in the anterior hypothalamic area (AHA) and medial basal (MBH) hypothalamus has been estimated (by the spectrofluorometric method) throughout the course of estrous cycle in the female rats. Serotonin content has been found to decrease significantly on the day of early and late proestrous in AHA and MBH, respectively. The involvement of serotonin in the process of regulation of gonadotropin releasing hormone(s) release on the level of AHA and MBH is discussed.

Activity of noradrenergic neurons of medial-basal hypothalamus of female rabbits in some stages of reproduction

Activity of noradrenergic neurons of medial-basal hypothalamus of female rabbits in some stages of reproduction. Acta Physiol. Pol., 1978, 29 (2): 111--115. The differences were found in the activity of noradrenergic neurons of medial-basal hypothalmus (MBH) estimated by the analysis of metabolism of intraventricularly infused 3H-noradrenaline (3H-NA) in various stages of reproduction in female rabbits. The gonadal hormones and especially 17beta-estradiol seem to be involved in this activity. The rapid disappearance of 3H-NA from MBH, found immediately after mating, implicates an involvement of noradrenaline in the process of Gn-RHs release form the rabbit hypothalamus.

Biosynthesis of the luteinizing hormone releasing hormone (LH-RH) in the rat hypothalamus

The biosynthesis of LH-RH was followed and evaluated in the hypothalamus of intact and castrated female rats after the infusion into the 3rd cerebral ventricle of L-3H-Glycine and its incorporation into the synthetized hormone. Incorporation of 3H-Gly into the LH--RH molecule that means biosynthesis of this hormone was found 30 min after the infusion of labeled amino acid. The incorporation rate in castrated animals was 2 times higher than in intact ones. Estradiol-17 beta only slightly depressed the LH--RH biosynthesis rate in castrated animals. Pretreatment with cycloheximide or puromycin decreased biosynthesis rate of the hormone by 50%. On the basis of cycloheximide and puromycin action it is suggested that the ribosomes are involved in the biosynthesis of LH--RH.

The hypothalamic centres involved in the control of production and release of prolactin in sheep

Lesions made in the anterior medial basal hypothalamus (MBH) in pregnant or lactating ewes caused lack of development of the mammary gland and depressed milk yield, a decrease in plasma prolactin concentration and structural changes in the prolactin cells as manifested by a lack of the expected degranulation (lack of the hormone release) or by atrophic changes and diminished cell granulation (or granule synthesis). Lesions made in the caudal MBH during pregnancy advanced development of the mammary gland, induced a rapid increase in the plasma prolactin concentration and caused extensive degranulation of prolactin cells. These results indicate that at least two functional systems controlling the secretion and production of prolactin exist in the hypothalamus of sheep: an anterior system which is stimulatory and a caudal which is inhibitory.

Noradrenaline turnover rate in the mediobasal and anterior hypothalamus of the rabbit

Noradrenaline turnover rate in the mediobasal and anterior hypothalamus of the rabbit. Acta Physiol. Pol., 1977, 28 (1): 39-43. The rate of noradrenaline (NA) turnover in mediobasal hypothalamus (MBH) and anterior hypothalamus (AH) of the rabbit was estimated by steady-state isotopic method with a tritiated noradrenaline (3H-NA) as a tracer. The disappearance rate of 3H-NA both in MBH and in AH was found to be biphasic; the first rapid phase of the NA half-life of about 30 min, followed by the second phase of slower decay of the half-life of 2.4 h and 10 h for MBH and AH respectively. The results suggest an existence of more than one metabolic pool of endogenous noradrenaline in MBH and AH and indicate regional difference in the metabolism of NA stores in the hypothalamus.

Role of catecholamines in release of gonadotrophic hormones in the rabbit

Role of catecholamines (CA) in transmission of neurohormone releasing gonadotrophin (GnHR) from the hypothalamus to hypophysis was estimated on the basis of the hypothalamic catecholaminergic system blockade with 6-hydroxydopamine (6-OHDA) and intraventricular infusions of CA in the rabbit. 6-OHDA administered intraventricularly in doses 200-500 mug caused temporary blockade of ovulation. Intraventricular infusion of noradrenaline (NA) induced ovulation in 50% of animals tested, whereas dopamine (DA) and adrenaline (A), induced ovulation only in very few cases. It seems, that catecholaminergic system participates in transmission of neurohormones to the hypophysis, and NA plays the most important role in this process.

The effects of indoleamines (serotonin and melatonin) on induction of ovulation in rabbits

Serotonin as well as melatonin introduced into the 3-rd cerebral ventricle in doses of 120 mug blocked induction of ovulation in rabbits; it was also observed that the ovulation-blocking effect of serotonin was much more effective than that of melatonin. The inhibitory effect of both indolamines on this process was more evident in summer than in spring. The role of serotonin and melatonin as mediators blocking the release of hypothalamic gonadotropin-releasing hormones (GRH) and the participation of these amines in the regulation of seasonal sexual rhythms are discussed.

Morphology of the prolactin producing cells in androgen-sterilized female rats

The aim of the study was to follow morphology of the prolactin producing cells in growing female rats with evoked "early androgen syndrome". The experiment was carried out on 3, 6 and 12-week-old animals. At the age of 3 weeks no changes in morphology of the prolactin cells were observed as compared to that of control animals. In 6 and 12-week-old animals the significant differences between androgenized and control animals were found. The prolactin cells differed both from those characteristic for normal females and normal males. The main characteristic features were: significantly smaller number of cells than in normal females, their stronger fluorescence and presence of large and giant prolactin cells similar to the so called "pregnancy cells". Possible factors responsible for the described above changes are discussed.

The effect and site of action of indoleamines on the hypothalamic centers involved in the control of LH release and ovulation in sheep

Serotonin or melatonin was infused into the 3rd cerebral ventricle (3rd V) or into the medial basal hypothalamus (MBH) of both intact ewes and ewes with lesions of the anterior hypothalamic area (AHA). Prolongation of the estrous cycle and delay of ovulation were obtained after infusions of melatonin or serotonin in both the intact and lesioned ewes. Statistically, serotonin proved to be more effective in this respect than melatonin in the intact ewes. The infusions also blocked the prevulatory peak of LH. Furthermore, the infusion of serotonin blocked estrous behavior, while that of melatonin did not affect this function. The effect of indoleamine infusions in the lesioned ewes, in which the inhibitory action of the AHA over the transmission of gonadotrophic releasing hormones (G-RH) had been eliminated, seems to indicate that the inhibitory action of indoleamines on the release of these neurohormones is being displayed at the level of the MBH.

Induction of ovulation in sheep by electrical stimulation of hypothalamic regions

Electrical stimulation of the anterior hypothalamus (regions of the supraoptic and anterior hypothalamic nuclei) or of the ventro-medial hypothalamus (infundibular or ventro-medial nuclei) during the last month of anoestrus in ewes induced ovulation within 72 hr., while similar stimulation of the same centres during the breeding season on the 12th day of the oestrous cycle did not advance ovulation. The role of the hypothalamic centres in the control of gonadotrophin secretion and ovulation is discussed in the light of these results.