Search PubMed⌕ Search

Biomedical subjects

G Fink

Publications and source records attributed to G Fink.

At least 199 records · Page 11Linked to original sources
PubMed1985

The priming effect of LH-releasing hormone: effects of cold and involvement of new protein synthesis.

The possible involvement of protein synthesis in the priming effect of LH-releasing hormone (LHRH) has been investigated in vitro using hemipituitary glands from pro-oestrous rats. Cycloheximide (7.1 mumol/l) blocked the priming effect of LHRH (elicited by 8.5 nmol LHRH/l) and protein synthesis (assessed by gel electrophoresis of 35S-labelled pituitary proteins). Pituitary glands were also incubated at 0-1 degrees C followed by incubation at 37 degrees C. While incubation at 0 degrees C for either 1 or 2 h reduced LH release and blocked protein synthesis, the LH response to LHRH in a subsequent 1-h incubation at 37 degrees C was similar to that during the corresponding period in pituitary glands incubated throughout at 37 degrees C. Incubation with medium alone at 0 degrees C during the first hour followed by incubation with LHRH at 37 degrees C during the second hour resulted in an LH response to LHRH which was similar to that in glands incubated with LHRH for 2 successive hours at 37 degrees C. Two-dimensional gel electrophoresis showed that LHRH priming was associated with the synthesis of a new protein of approximately 69 000 molecular weight and with changes in the isoelectric point of two other high molecular weight proteins. These results suggest that the priming effect of LHRH involves the synthesis of a new protein as well as post-translational changes (possibly phosphorylation) in two other proteins and that exposure to cold may prime the pituitary gland to LHRH possibly by stimulating intracellular Ca2+ release and/or protein phosphorylation.

Animals↗
PubMed1985

Effect of immunoneutralization of thyrotrophin-releasing hormone on the release of thyrotrophin and prolactin during suckling or in response to electrical stimulation of the hypothalamus in the anaesthetized rat.

The aim of the present study was to use the technique of immunoneutralization with anti-thyrotrophin-releasing hormone (anti-TRH) serum to investigate the role of TRH in mediating the TSH and prolactin responses to electrical stimulation of the hypothalamus and the prolactin response to suckling in lactating rats. Electrical stimulation of either the median eminence or paraventricular nuclei of male or female rats anaesthetized with urethane resulted in significant increases in the plasma concentrations of both TSH and prolactin. Injection of sheep anti-TRH serum blocked the rise in plasma TSH concentration in response to stimulation of either brain area, but did not block the increase in plasma prolactin concentration. In anaesthetized, lactating female rats, the suckling stimulus produced a significant increase in the plasma prolactin concentration, but did not alter the plasma TSH concentration. Injection of anti-TRH serum, but not control non-immune or anti-bovine serum albumin, significantly decreased the basal release of TSH but did not abolish the prolactin response to suckling. These results show that TRH is the principal mediator of the neural control of TSH release in the rat, but is not crucial for the release of prolactin in response to either hypothalamic stimulation or suckling.

Animal Population Groups↗
PubMed1985

The role of microfilaments in the priming effect of LH-releasing hormone: an ultrastructural study using cytochalasin B.

We have investigated the possibility that microfilaments are involved in the priming effect of LH-releasing hormone (LHRH) by ultrastructural morphometry of hemipituitary glands from adult female mice. Glands incubated for 2 consecutive hours with 8.5 nmol LHRH/l responded with a marked increase in the amount of LH released into the medium during the second hour compared with the first hour of incubation. This priming effect of LHRH on LH secretion was accompanied by a significant margination of secretory granules and a drop in the total granule content of the gonadotrophs. Although the number of microfilaments remained the same, there was an increase in their length and a change in orientation so that the angle between the microfilaments and the plasmalemma was significantly reduced after both the first and second hour of exposure of LHRH. The addition of 14.3 mumol cytochalasin B/1 to the incubation medium significantly increased the amount of LH released in the first hour of incubation when compared with the amount of LH released by LHRH alone, but completely abolished the priming effect of LHRH. Cytochalasin B also prevented the LHRH-induced increase in the length and the change in orientation of the microfilaments. These results indicate that LHRH priming involves an increase in length of microfilaments and a change in their orientation relative to the plasmalemma.

Animals↗
PubMed1985

Vasoactive intestinal peptide in rat hypophysial portal blood: effects of electrical stimulation of various brain areas, the oestrous cycle and anaesthetics.

Vasoactive intestinal peptide (VIP) was measured by radioimmunoassay in hypophysial portal and peripheral blood from adult male and female Wistar rats. The results confirmed that the concentration of VIP in hypophysial portal blood was significantly greater than in peripheral blood and showed that VIP release into portal blood was not affected by removal of the gut, the largest peripheral source of VIP. Electrical stimulation of the median eminence, several hypothalamic nuclei, the amygdala or hippocampus had no significant effect on the release of VIP into portal blood, possibly because under the conditions of the experiment the spontaneous release of VIP is already at a maximum. In female rats, the VIP released into portal blood collected between 13.00 and 18.30 h of each day of the 4-day oestrous cycle varied under different anaesthetics, and there was no consistent increase in VIP release on pro-oestrus suggesting that VIP is not involved in the pro-oestrous surge of prolactin.

Anesthetics↗
PubMed1984

Effect of mating on the metabolic activity of the brain and pituitary gland assessed by [14C]2-deoxyglucose in a reflex ovulator, the vole (Microtus agrestis).

The neural pathways involved in reflex ovulation in the vole (Microtus agrestis) have been investigated with the [14C]2-deoxyglucose (2-DG) method. Female voles were injected i.p. with 2-DG and either not mated, sham-mated (mounted by males by vagina was taped) or mated for a period of 45 min after the injection, after which the animals were decapitated. The brain was processed for autoradiography and the relative metabolic activities (rma) of selected areas of the brain and pituitary gland were determined. The plasma separated from trunk blood was assayed for the concentration of luteinizing hormone (LH). The lordosis quotients (LQ) were (mean +/- S.E.M.) 81 +/- 8 (n = 5) in mated compared with 47 +/- 8 (n = 5) in sham-mated voles. The rma of the midbrain central grey (CG) and reticular formation (RF) were significantly greater in mated and sham-mated voles compared with the values in unmated voles. There were no other between-group differences in the rma of the other 28 areas of the brain or pituitary gland studied in spite of the fact the plasma LH concentration in mated voles was 36.9 +/- 9.6 ng NIH-LH-S18/ml compared with undetectable (less than 2.5 ng/ml) values in all the sham-mated and unmated animals. These results show that in the vole increased metabolic activity of the CG and RF is associated with lordosis, but that the reflex release of LH is not accompanied by any significant change in the metabolic activity of the brain or the pituitary gland.

Animals↗
PubMed1984

A hypothalamic-pituitary system that stimulates the release of plasminogen activator in the rat.

We have studied the possible role of the hypothalamic-pituitary system in the control of the release of plasminogen activator (PA) into peripheral blood of male rats. Plasminogen activator was measured by euglobulin lysis time. Desamino-D- arginine vasopressin (dDAVP) and adrenaline injected i.v. induced an increase in plasma PA as did electrical stimulation of the median eminence (ME), but dDAVP had no effect on plasma PA in hypophysectomized rats. The PA response to ME stimulation was similar in Brattleboro rats (deficient in vasopressin) and adrenalectomized Wistar rats compared with intact Wistar rats, but was abolished by section of the pituitary stalk and was negligible in hypophysectomized rats. The 41-residue corticotropin releasing factor (CRF) had no effect on PA release. Saline extracts of anterior pituitary gland from both normal Wistar and Brattleboro rats produced a dose-dependent increase in plasma PA when injected into normal Wistar rats. The activity of pituitary tissue was abolished by boiling, but not by di-isopropyl fluorophosphate which inactivates PA itself. Thus the anterior pituitary gland of the rat contains a heat-labile factor which stimulates the release of PA from peripheral stores into the circulation. This pituitary factor is released by a hypothalamic factor that is neither vasopressin nor CRF.

Animals↗
PubMed1984

Somatostatin-28(1-12)-like immunoreactive substance is secreted into hypophysial portal vessel blood in the rat.

Somatostatin-28(1-12)-like immunoreactivity was measured in extracts of rat hypophysial portal blood and peripheral blood. The concentration of somatostatin-28(1-12) was higher in portal than in peripheral extracts, and its release into portal vessel blood was increased 4- to 5-fold by electrical stimulation of the median eminence. These results show that somatostatin-28(1-12) may be a physiological neurohormone and/or neurotransmitter.

Animals↗
PubMed1984

Comparison of the effects of Althesin and sodium pentobarbitone on the regional uptake of 2-deoxyglucose by the brain and pituitary gland of the rat: selective effects on pars intermedia.

The uptake of radiolabelled 2-deoxyglucose (2DG) was used to compare the effects of the steroid anaesthetic, Althesin (alphaxalone plus alphadolone acetate) with those of sodium pentobarbitone on the regional metabolism of the brain and pituitary gland. Experiments were carried out on adult female Wistar rats. Studies on conscious animals were carried out with the aid of an indwelling intra-atrial catheter. The uptake of 2DG was measured both by liquid scintillation spectroscopy of 3H-2DG in tissue blocks and by quantitative autoradiography with 14C-2DG. Both anaesthetics significantly reduced uptake of 3H-2DG in the frontal, parietal and occipital cortex, and striatum and thalamus, but 3H-2DG uptake was significantly increased in the pituitary gland. Similar effects were found by measuring 14C-2DG uptake, and this technique showed further that Althesin, but not sodium pentobarbitone, selectively increased (2-fold) the uptake of 14C-2DG by the pars intermedia. The increase in 14C-2DG uptake by the pars intermedia in animals anaesthetized with Althesin was significantly reduced by a lesion placed in the arcuate nucleus. The most likely explanation for the effects of Althesin on the pars intermedia is that this anaesthetic increases the activity of arcuate neurons that innervate the pars intermedia.

Alfaxalone Alfadolone Mixture↗
PubMed1984

Pulsatile luteinizing hormone release, and the inhibitory effect of estradiol-17 beta in gonadectomized male and female rats: effects of neonatal androgen or exposure to constant light.

The characteristics of pulsatile LH release and the acute inhibition of LH release by estradiol-17 beta (E2) were studied in long term (21 days) gonadectomized female and male Wistar rats. Three groups of female rats were examined; animals exposed either to summer lighting (14-h on; 10-h off; LD) or continuous illumination (LL) and animals treated neonatally with testosterone propionate (TP) and exposed to LD. The mean plasma LH concentrations and interpulse intervals were similar in both male and LD female rats. However, treatment of female rats with TP or exposure to LL reduced the mean plasma LH concentration in female rats and increased the interpulse interval when compared with LD female or male rats. The amplitude of the LH pulses was significantly greater in the LD female rats compared with those in the male rats; since pituitary responsiveness to a single iv injection of 50 ng LHRH/100 g BW was similar in the two groups, this suggests that the amount of LHRH released per pulse of LH is greater in the female than in the male. The greater amplitude but similar frequency of LH pulses in the LD female compared with the LD male suggest that the MCR of LH may be greater in the female. The pulse amplitude in the TP-treated rats was similar to that in the rats exposed to LL and since pituitary responsiveness to LHRH was significantly greater in the TP rats, there was probably more LHRH released per pulse of LH in the LL-treated rats. Pituitary responsiveness to LHRH was significantly lower in the LL- and TP-treated rats compared with males and LD females. The timing of the inhibition of LH secretion by E2 was similar in all four groups of animals, and in LD females was not affected by a 92% depletion of serotonin, 100% depletion of 5-hydroxyindoleacetic acid, or a 33% depletion of dopamine in the hypothalamus produced by the administration of parachlorophenylalanine.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗
PubMed1984

The hypogonadal mouse pituitary contains bioactive LH.

Saline extracts of pituitary glands from normal and hpg male mice were assayed for LH by the testosterone production assay. The extract of hpg pituitary tissue stimulated testosterone production by mouse Leydig cells in a dose-dependent manner which paralleled that of normal mouse pituitary. The normal mouse pituitary was about 20 times as potent as hpg pituitary which is similar to the relative potency obtained by radioimmunoassay. These results show that differentiation of the gonadotrophs and the synthesis of some biologically active LH can occur in the absence of LHRH.

Animals↗
PubMed1984

Effects of acute administration of 2-hydroxylated metabolites of oestrogens on LH and prolactin secretion in male and female prepubertal rats.

The effects of catechol oestradiol and catechol oestrone on the release of LH and prolactin were investigated in immature male and female Wistar rats. In male rats both catechol oestradiol and catechol oestrone significantly increased the plasma concentration of LH, and catechol oestradiol but not catechol oestrone significantly increased the plasma concentration of prolactin and decreased the pituitary concentration of LH. The parent oestrogens, oestradiol-17 beta and oestrone, had no effect on plasma LH concentrations, but both increased significantly the plasma concentration of prolactin, and oestrone but not oestradiol-17 beta increased the pituitary concentration of LH. In immature female rats, catechol oestradiol inhibited the surge of LH and the increase in uterine weight induced by injecting pregnant mare serum gonadotrophin (PMSG). The injection of oestrone induced an increase in the plasma concentration of LH which was about nine times greater than that produced by oestradiol-17 beta. There were no significant differences in the effects of these steroids on plasma prolactin concentration. These results (i) confirm that in the immature male rat catechol oestrogens can stimulate LH release and show that catechol oestradiol can increase prolactin release, (ii) show that catechol oestradiol can inhibit the stimulatory effects of PMSG on LH release and uterine weight in the immature female rat, and (iii) demonstrate that oestrone can stimulate LH release in the immature female rat.

Animals↗
PubMed1983

The human hypothalamic LHRH precursor is the same size as that in rat and mouse hypothalamus.

The synthesis of the decapeptide luteinizing hormone releasing hormone (LHRH) in human, rat and mouse brain has been investigated by studying the in vitro translation products of Poly A+ mRNA extracts from the hypothalamus. The translation products of all three species contained a single 28000 MW polypeptide which immunoprecipitated with a specific anti-LHRH serum. This polypeptide was not present in the translation products of Poly A+ mRNA extracts from the hypothalamus of the hypogonadal mouse, a mutant strain totally deficient in LHRH. These results show that in the human, rat and normal mouse, LHRH is synthesized as a component of a precursor peptide with a molecular weight of 28000.

Aged↗
PubMed1983

The milk ejection pathway in brain studied with the 2-deoxyglucose method.

The neural pathways involved in the milk ejection reflex have been studied with the aid of the 2-deoxyglucose (2DG) method. All the experiments were carried out on Wistar female rats, 9-11 days post-partum, which had been separated from their pups (except for one) overnight. The effect of suckling on the relative metabolic activity (RMA) of the brain was studied in conscious rats and in rats anaesthetized with urethane. Control animals were similarly treated but were not suckled. In addition, the effect of mammary nerve stimulation on RMA was studied in animals anaesthetized with urethane; sham-operated animals served as controls for this group. Suckling (minimum of 10 pups) in conscious animals had no apparent effect on the RMA of any of the brain areas measured. However, in anaesthetized rats, suckling produced a significant increase in the RMA of the paraventricular and supraoptic nuclei (PVN and SON), but had no effect on the RMA of any other brain area or the pituitary gland. Stimulation of the mammary nerve, with a stimulus that causes milk ejection and an increase in prolactin release, produced a significant increase in the RMA of the PVN, SON, the pars distalis and pars nervosa and the spinothalamic tract, and a significant decrease in the ventromedial and mediodorsal nuclei of the thalamus, the zona incerta, the red nucleus and the ventral nucleus of the lateral lemniscus. These results show that suckling significantly increases the metabolic activity of afferent terminals in the PVN and SON. Activation of the cell bodies of the PVN and SON, as assessed by increased RMA of the pituitary gland, could be evoked by the more intense stimulus of mammary nerve stimulation. The ascending pathway from the mammary nerve involves the spinothalamic tract but could not be traced beyond the midbrain. The lack of effect of suckling in conscious animals may have been due to the inhibitory influence of stress mediated by forebrain structures.

Animals↗
PubMed1983

Water deprivation results in increased 2-deoxyglucose uptake by paraventricular neurones as well as pars nervosa in Wistar and Brattleboro rats.

The [14C]2-deoxyglucose (2-DG) technique has been used in conjunction with quantitative autoradiography to determine the metabolic activity of the neurones of the hypothalamo-neurohypophysial system. Water deprivation (4 days) in Wistar rats led to a more than two-fold increase in the metabolic activity of the pars nervosa (PN), and a significant increase in the metabolic activity of paraventricular (PVN) but not supraoptic (SON) neurones. The PN in homozygous Brattleboro rats was significantly more active than that in hydrated Wistar and Piebald Virol Glaxo (PVG) rats; as in Wistar rats, activity of the PN and PVN was significantly increased by 12-15 h water deprivation. The administration of desamino-D-arginine vasopressin (dDAVP) to Brattleboro rats significantly reduced the activity of the PN to that seen in hydrated Wistar and PVG rats. This reduction in activity was accompanied by a significant reduction in plasma osmolality. These results show that (1) in contrast to studies in which the osmotic stimulus was a salt load, water deprivation leads to a significant increase in 2-DG uptake by the perikarya as well as the terminals of neurohypophysial neurones; (2) increased activity of the neurohypophysial neurones occurs even when there is a genetic deficiency of vasopressin and the activity can be increased further by an osmotic stimulus, and (3) the activity of the neurohypophysial neurones can be significantly reduced by the administration of dDAVP.

Animals↗
PubMed1983

Somatostatin-28 is an hormonally active peptide secreted into hypophysial portal vessel blood.

Somatostatin 14 and 28 (SS-14 and SS-28) have been measured in hypophysial portal blood of male Wistar rats. The concentration and total amount of SS released into portal blood were increased 6- to 7-fold by electrical stimulation of the median eminence. On HPLC, only two peaks of immunoreactivity were detected in extracts of portal plasma and these peaks corresponded with SS-14 and SS-28, respectively. The amount of SS-28 in portal plasma was, on a molar basis, similar or greater than that of SS-14 and this together with other evidence suggests that SS-28 is an hormonally active peptide.

Animals↗
PubMed1983

Neuropeptide--receptor interactions studied with the aid of fluorescence-activated cell sorting and video intensification microscopy.

Studies of interactions between neurotransmitters and their receptors would be greatly facilitated by a method for obtaining cell fractions enriched with cells that contain a high density of receptors specific for the neutrotransmitter. Here we report the use of a fluorescence-activated cell sorter (FACS) to prepare fractions of pituitary cells that contain a high density of specific receptors for the decapeptide, luteinizing hormone-releasing hormone (LHRH). The fluorescence probe, an agonist of LHRH coupled to rhodamine isothiocyanate [(rhod-D-Lys6)-LHRH], was 75% as potent as LHRH in terms of releasing LH from dispersed pituitary cells. Cells, dispersed mechanically from the anterior pituitary glands of either immature rats or ovariectomized rats treated with oestrogen and progesterone, were exposed to (rhod-D-Lys6)-LHRH at 4 degrees C for 1 h and passed through a FACS. The pituitary cells sorted into two major peaks, one of which contained cells that fluoresced brightly and showed a significant LH response to LHRH, and a second which contained cells that did not fluoresce and showed no LH response to LHRH. Using photon counting techniques, the population of fluorescent cells was found to bind LHRH in a saturable and specific manner. In the immature rats the percentage of the large cell population that bound (rhod-D-Lys6)-LHRH was about 80%, approximately the same proportion of the cell population that is made up of gonadotrophs.

Animals↗
PubMed1983

Uptake and release of [3H]dopamine by the median eminence: evidence for presynaptic dopaminergic receptors and for dopaminergic feedback inhibition.

The accumulation and release of [3H]dopamine by the median eminence in vitro was studied after treatments with different pharmacological agents, to determine whether such a procedure would be useful for measuring neuronal activity in the tuberoinfundibular dopaminergic system. The accumulation of [3H]dopamine was temperature, time, and sodium dependent, and reduced by unlabelled dopamine and by a potent dopamine uptake blocker, nomifensine. The outflow of tritium was studied after blocking the oxidative deamination of dopamine by nialamide. The outflow of tritium was elicited consistently by biphasic square wave electrical pulses and by high molarity potassium ions. The response to electrical stimulation was dependent largely on calcium and partially on sodium. The response to high molarity potassium ions was reduced in the absence of calcium ions. The response to electrical stimulation was increased by nomifensine and by a dopaminergic antagonist, haloperidol, and was reduced by dopamine and by a dopaminergic agonist, piribedil. The inhibitory action of dopamine was antagonized by haloperidol. These results indicate the existence of uptake and release mechanisms in the tuberoinfundibular dopamine neurons, and suggest that dopamine may inhibit its own release via dopaminergic receptors. This in vitro method may be useful for measuring dopamine uptake and release by tuberoinfundibular dopaminergic neurons.

Animals↗