Possible role of dopamine as transmitter to promote discharge of LH-releasing factor

Plasma concentration of gonadotrophins, oestrogens and progesterone in thyrotoxic women

Plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), oestrogen and progesterone were measured daily in 15 thyrotoxic women in the reproductive age for 28 to 30 consecutive days before commencement of therapy and for a similar period following restoration of the euthyroid state. Five of these patients had secondary amenorrhoea whilst the other 10 had hypomenorrhoea. Twelve healthy volunteer eythyroid women of similar age and parity, with no history of menstrual abnormality, served as controls. The levels of both gonadotrophins (LH and FSH) and oestrogen were found to be significantly raised in all thyrotoxic patients in comparison with levels in the euthyroid female controls (P less than 0.001). "Mid cycle" LH and FSH peaks were present in thyrotoxic patients who were still menstruating whilst they were absent in those who developed amenorrhoea. Plasma oestrogen concentration rose to a peak on the day before the surge of LH (and FSH) in all euthyroid frmale controls as well as in thyrotoxic patients who were still menstruating. In contrast, oestrogen peaks occurred without ensuing LH (and FSH) peaks in thyrotoxic patients who had developed amenorrhoea, suggesting a failure of the positive feed-back mechanism. The levels and patterns of plasma progesterone in thyrotoxic subjects who were still menstruating were similar to those of euthyroid controls. However, no significant circulating plasma progesterone was detected in thyrotoxic subjects who were amenorrhoeic. The levels and patterns of all of these hormones (gonadotrophins, oestrogen and progesterone) became normal after restoration of euthyroid state and normal menstruation.

Stimulation electrically and by acetylcholine of the rat hypothalamus in vitro

1. The hypophysiotrophic area of the rat hypothalamus was studied in vitro. The preparation remained viable for at least 3 hr and showed oxygen consumption varying between 68.9-120 mumole/g.hr. The tissue potassium ion content (per unit wet weight) fell to about 50% of the in vivo concentration during this time compared with 15% in the presence of ouabain (10(-4) M). Histological examination of tissue incubated for 3 hr showed variable perineuronal oedema but the nuclei were of normal appearance and none showed the pyknotic changes that would be associated with cell degeneration.2. Corticotrophin releasing hormone (CRH) in the medium pooled from five to twenty hypothalami was assayed in five to twelve rats which were median-eminence lesioned 48 hr earlier. In vitro corticosterone production of quartered adrenals was used as the end point of the assay. Regression lines of the dose-response curves for ACTH, crude CRH and different volumes of medium from electrically stimulated hypothalami were parallel. CRH output was maximal at 75 Hz and 100 muA when the square-wave pulses lasted for 1 msec. No CRH activity was found on stimulation of cerebral cortex or thalamic tissue pieces of equivalent size.3. Hypothalami taken from rats, adrenalectomized 7-14 days previously, released several-fold more CRH into the medium during electrical stimulation than the initial content of the tissue, showing that the tissue was capable of synthesizing CRH in vitro. The hypothalami taken from intact rats released considerably less CRH into the medium than tissue taken from 12 to 14 day adrenalectomized rats. The hyper-secretion of CRH observed in hypothalami taken from adrenalectomized rats was abolished by pre-treatment with 5 mg/100 g s.c. of corticosterone 24 hr before removal of the tissue. It is therefore proposed that the delayed negative feed-back action of corticosterone at the hypothalamic level is by the suppression of CRH synthesis and that the effect of secretion is secondary to the effect on synthesis.4. The presence of Ca(2+) in the medium was essential for the release of CRH.5. CRH secretion increases linearly with doses of acetylcholine from 5.5 x 10(-15)-5.5 x 10(-14) M. Cerebral cortex incubated with acetylcholine showed no CRH activity. The effect of acetylcholine was reduced by atropine (3.5 x 10(-13) M). Median eminence-pituitary stalk fragments (which contain mainly terminal axons of neurones) incubated with acetylcholine showed no CRH stimulation in the doses that activate the release of CRH using the hypophysiotrophic hypothalamus. Acetylcholine may act as a neurotransmitter at the dendritic level in the CRH neurone.

Dopamine synthesis: stimulation by a hypothalamic factor

The effect of treatment with the factor that inhibits the release of melanocyte stimulating hormone (MSH) identified as 1-prolyl-1-leucylglycinamide (MIF) on brain catecholamine synthesis was examined in normal and hypophysectomized rats. The tripeptide induced a dose-related increase in striatal dopamine synthesis in slices obtained from treated normal animals but not in hypophysectomized animals. Hypothalamic norepinephrine synthesis was unaltered by MIF treatment in normal as well as in hypophysectomized rats. In addition, dopamine and norepinephrine syntheses were depressed in untreated hypophysectomized animals, as compared to normal controls. These results constitute the first direct demonstration of a central neurochemical effect of a hypothalamic factor.

Hypothalamic regulatory hormones

The molecular structures of several polypeptides isolated from hypothalamic tissue have been established and the synthesis of these compounds has been achieved. These polypeptides selectively stimulate or inhibit the release of anterior pituitary hormones and melanocyte-stimulating hormone. Various studies indicate their important physiological role and support the concept that some of these polypeptides are hormones. Some synthetic hypothalamic hormones and their derivatives may find important clinical and veterinary applications.

Stimulation of tubero-infundibular dopamine neurones and gonadotrophin secretion

1. In ovariectomized rats pre-treated with oestrogen and progesterone, the intensity of the catecholamine fluorescence was determined by micro-fluorimetry in the cell bodies of the tubero-infundibular dopamine neurones (situated in the arcuate and periventricular hypothalamic nuclei). The concentrations of follicle-stimulating (FSH) and luteinizing hormone (LH) in serum and pituitary were estimated by bio-assay.2. The characteristic changes in fluorescence intensity of the tuberal catecholamine-containing nerve cell group that are induced by unilateral intermittent electrical stimulation of the arcuate nucleus or of the medial preoptic area during 5-60 min, were accompanied by a marked rise in serum LH concentration. With arcuate stimulation, the rise in serum LH paralleled the increase in the fluorescence intensity of the nerve cell bodies, whereas with preoptic stimulation, the initial increase in cellular fluorescence intensity preceded the rise in serum LH. Preoptic stimulation also caused a moderate fall in pituitary LH which was simultaneous with the increase in fluorescence intensity. No systematic changes in FSH concentration were observed during the time interval studied.3. Pre-treatment with the tyrosine hydroxylase inhibitor alpha-methyltyrosine completely blocked the increase in fluorescence intensity caused by electrical stimulation of the arcuate nucleus but did not prevent the rise in serum LH.4. It is concluded that the tubero-infundibular dopamine neurones serve as an intermediary between the medial preoptic area (and possibly other forebrain structures) and neurones containing releasing factors. Under the present experimental conditions, stimulation of the tuberoinfundibular dopamine neurones increased the release of LH, probably by promoting the release of LH-releasing factor.

Monoamines and ovarian hormone-linked sexual and emotional changes: A review

Emotional upsets related to changes in ovarian hormones are highly prevalent and are responsible for psychiatric morbidity and mortality. Significant increases in acute psychiatric hospitalizations, suicidal activity, and other psychopathology occur during the premenstruum and during menstruation. This paper reviews evidence indicating that menstrual cycle psychopathology may be mediated by the effects of estrogen, progesterone, and possibly the renin-angiotensin-aldosterone system on the brain monoamines, norepinephrine, dopamine, and serotonin. During the menstrual cycle, psychopathology often begins with the onset of luteal estrogen-progesterone-angiotensin-aldosterone secretion and intensifies as these hormone levels later fall, prior to and during menstruation. Aldosterone is reported elevated in cases of premenstrual tension syndrome. There are numerous reports of affective upsets occurring with the use of estrogen-progestin oral contraceptives and following their withdrawal. Contraceptives stimulate the renin-angiotensin-aldosterone system and are reported useful in alleviating premenstrual-menstrual emotional upsets and postpartum depressive episodes. Affective lability, prevalent at parturition, occurs when estrogen, progesterone, and aldosterone levels are first high and later falling. Exogenous estrogen and progesterone profoundly affect mating activity in castrated rhesus monkeys, and cyclic fluctuations in sexual activity in humans may occur during the menstrual cycle. Much information links manic and depressive reactions with alterations in brain monoamines. Lithium, monoamine oxidase inhibitors, and tricylic antidepressants, specifically used to treat affective disorders, are reported useful in treating ovarian hormone-linked upsets. Similarities exist between changes in animal behavior caused by drugs altering affective states and the effects of ovarian hormones. Like certain antidepressants, estrogen induces hyperactivity in rats. Like reserpine, progesterone exhibits sedative and soporific effects. Sexual behavior in female rats is reported linked to changes in brain monoamines. Agents increasing brain monoamine levels and availability decrease mating responses, and monoamine depletors, such as reserpine may be substituted for progesterone in activating mating behavior. Serotonin and dopamine appear to be important in the regulation of ovulation. Brain norepinephrine varies with the phases of the rat estrus cycle. Castration increases brain norepinephrine and decreases brain dopamine. Exogenous estrogen decreases rat brain norepinephrine content. The monoamine-destroying enzymes, monoamine oxidase, and catechol O-methyl transferase are affected by ovarian steroids and show fluctuating levels during the reproductive cycle. The effects of reserpine, monoamine oxidase inhibitors, tricyclic antidepressants, and lithium on monoamines in neurophysiological preparations have been used as evidence supporting theories linking monoamine changes with human affective disorders. Estrogen, progesterone, and angiotensin also exhibit effects on in vitromonoamine systems. Like the tricyclic antidepressants, uptake of norepinephrine and dopamine by nerve endings is inhibited in the presence of estrogen, progesterone, and angiotensin. As with reserpine, the flow of these monoamines from nerve endings is increased by progesterone. Estrogen slows the flow of norepinephrine from nerve endings and decreases the electrically induced release of serotonin and norepinephrine from brain slices. The above information provides clues that ovarian hormone-linked psychopathology, like affective disorders in general, may be related to alterations in brain monoamines.

Effect of adrenergic-blocking or -stimulating agents on plasma growth hormone, immunoreactive insulin, and blood free fatty acid levels in man

In order to determine whether an adrenergic mechanism is involved in the secretion of growth hormone and insulin, the effect of adrenergic-blocking or -stimulating agents on plasma human growth hormone (HGH), immunoreactive insulin, blood free fatty acids (FFA), and glucose levels was studied in normal human subjects. The intravenous infusion of propranolol, a beta adrenergic-blocking agent, caused a rise in plasma HGH, a transient decrease in blood FFA, and no significant change in plasma insulin. This increase in plasma HGH was inhibited either by the combined administration of isoproterenol, a beta adrenergic-stimulating agent, along with propranolol or by oral glucose loading immediately before the start of propranolol infusion. The concomitant administration of epinephrine and propranolol brought about a rise in plasma HGH comparable with that produced by propranolol alone, without any significant change in blood FFA. Alpha adrenergic blockade by the intravenous infusion of phenotolamine significantly suppressed plasma HGH responses to insulin-induced hypoglycemia and to arginine infusion, and enhanced plasma insulin response to arginine infusion. It also stimulated lipid mobilization significantly. The intravenous infusion of alpha adrenergic-stimulating agents, phenylephrine and methoxamine, caused an increase in plasma HGH, a slight decrease in blood FFA, and no significant change in plasma insulin. This increase in plasma HGH was significantly inhibited by the simultaneous administration of phentolamine along with methoxamine. On the contrary, a beta adrenergic stimulant, isoproterenol, raised plasma insulin and blood FFA, and abolished the plasma HGH response to propranolol. Another beta stimulator, isoxsuprine, raised blood FFA but not plasma insulin. It is concluded that either beta adrenergic blockade or alpha stimulation enhances HGH secretion and inhibits insulin secretion and fat mobilization, whereas either alpha blockade or beta stimulation stimulates insulin secretion and fat mobilization and inhibits HGH secretion.