Jacob Kraicer

Biological and Radioimmunological Evidence for Melanocyte Stimulating Hormones (MSH) of Extrapituitary Origin in the Rat Brain

The possible existence of extrapituitary melanocyte stimulating hormone (MSH) in various regions of the rat brain has been studied in intact and hypophysectomized rats. Using a sensitive and specific radioimmunoassay (RIA), alphaMSH has been found in a number of brain regions in intact rats. The standard curves of synthetic alphaMSH and the dilution curves for pars intermedia nervosa (PIN), pars distalis (PD), hypothalamus and thalamus extracts were strictly parallel. The alphaMSH concentrations were measured in PIN (6,225 +/- 962 ng/mg wet tissue); PD (12.5 +/- 1.41 ng/mg); pineal (380 +/- 29 ng/g wet tissue); hypothalamus (645 +/- 161 ng/g) and thalamus (33.3 +/- 5.26 ng/g). In rats hypophysectomized for 1 or 2 months, the highest concentrations of immunoreactive alphaMSH were found in pineal (353 +/- 140 ng/g wet tissue), hypothalamus (85.8 +/- 14.1 ng/g) and thalamus (39.8 +/- 13.9 ng/g). Hypophysectomy significantly reduced hypothalamic MSH content and concentration but did not alter MSH concentration in pineal and thalamus. From these results, we conclude that hypothalamic alphaMSH is, in part, of hypophyseal origin while pineal and thalamus alphaMSH does not originate from the pituitary. After Sephadex G-25 gel filtration, synthetic alphaMSH and PIN extracts showed a single peak of both bioactive and immunoreactive alphaMSH. In the same conditions, extracts from the 5 brain regions studied in hypophysectomized rats chromatographed as a single peak of immunoreactive MSH but as 2 peaks of apparent bioactive MSH, 1 concident with synthetic alphaMSH and the other far after the salt volume. We conclude that alphaMSH is found in a number of brain areas and its presence after hypophysectomy would indicate synthesis within the central nervous system.

Pars Intermedia and Pars Distalis:Two Sites of ACTH Production in the Rat Hypophysis

Pars intermedia and pars distalis of the rat hypophysis were examined, following experimentally induced alterations in ACTH secretion. The concentration of ACTH in the pars inter-media is considerably

Differential Control of the Release of Pro-Opiomelanocortin-Derived Peptides from the Pars intermedia of the Rat Pituitary

The pars intermedia (PI) of the adenohypophysis synthesizes pro-opiomelanocortin, which, through post-translational processing, gives rise to a group of chemically related peptides, including αMSH, AC

Release of Pro-Opiomelanocortin-Derived Peptides from the Pars intermedia and Pars distalis of the Rat Pituitary: Effect of Corticotrophin-Releasing Factor and Somatostatin

The parenchymal cells of the pars intermedia (PI) and corticotrophs of the pars distalis (PD) synthesize pro-opiomelanocortin (POMC), which, through posttranslational processing, gives rise to a group of structurally related peptides, including MSHs, ACTH, CLIP, LPHs and endorphins. We investigated the control of release of these peptides using an in vitro system. We perifused either intact neurointermediate lobes (NI) or PD halves obtained from rats. Perifusion medium and tissue extracts were subjected to a battery of bioassays (BA) and radioimmunoassays (RIA) (including MSH-BA, alpha-MSH-RIA, ACTH-BA, ACTH-RIA, LPH-RIA) and a receptor-binding assay for morphine-like activity (MLA). The relative amounts of released peptide activities were examined under basal conditions and after challenging with synthetic ovine corticotrophin-releasing factor (CRF) and somatostatin. CRF stimulated the release of all assayed peptides from both the PD and PI in a dose-related manner. Stimulated release was immediate (within 3 min), constant, reversible and repeatable. Somatostatin (up to 100 ng/ml) did not alter basal release from either PD or PI. Somatostatin did block CRF-induced release from the PI but not from the PD. These observations support an action of both CRF and somatostatin in the control of secretion of POMC-derived peptides from the PI.

In vitro Release of ACTH from Dispersed Rat Pars Intermedia Cells. II. Effect of Neurotransmitter Substances

Studies were carried out to test the responsiveness of dispersed pars intermedia (PI) cells to a number of neurotransmitter substances known to be present in the PI. These substances were tested over an extended dose range. The catecholamines, adrenaline, noradrenaline, and dopamine inactivated PI ACTH at high concentrations; at lower concentrations, they were without effect. Histamine and carbachol had no effect on ACTH release. 5-hydroxytryptamine stimulated ACTH release in a dose-related manner, from 10(-6) to 10(-3)M, while having no effect on ACTH release from the pars distalis (PD). We conclude that the release of ACTH from the PI may be controlled by direct serotonergic innervation.

LHRH radioimmunoassay and its applications: Evidence of antigenically distinct FSHRH and a diurnal study of LHRH and gonadotrophins

Abstract A sensitive and specific radioimmunoassay for LH-releasing hormone (LHRH) was developed. Using a specific antibody we have attempted to define or dissociate a separate FSHRH, antigenically distinct from LHRH. In an in vitro system, LH release by hypothalamic extract was inhibited by a certain dose of LHRH antiserum but FSH release was not affected. Diurnal patterns of LHRH, FSH and prolactin were studied but no clear cyclic changes were shown. LHRH and LH levels in the serum were completely dissociated. We suggest that negative feedback systems play a more critical role than hypothalamic LHRH in the release of LH.

Dopaminergic Mediation of the Effect of Elevated Potassium on the Release of Pro-Opiomelanocortin-Derived Peptides from the Pars intermedia of the Rat Pituitary

The pars intermedia (PI) of the adenohypophysis synthesizes pro-opiomelanocortin (POMC), which through post-translational processing, gives rise to a group of chemically related peptides, including αM

Thyrotropin-Releasing Hormone Does Not Alter the Release of Melanocyte-Stimulating Hormone or Adrenocorticotropic Hormone from the Rat Pars intermedia

Thyrotropin-releasing hormone (TRH) has been reported to stimulate the release of melanocyte-stimulating hormone (MSH) from the pars intermedia (PI) of Rana esculenta. To test its effect on the rat PI, acutely dispersed rat PI cells, as well as whole nervosa-intermedias (NI), were incubated with synthetic TRH, from 10(--10)--10(--4)M. TRH did not alter the release of either MSH or adrenocorticotropic hormone (ACTH).

Electrical changes induced in rat adenohypophysial cells, in vivo, with hypothalamic extract.

Intracellular recording techniques havebeen used to measure transmembrane potentials (TMP), membrane resistance, and membrane capacitance from individual cells in the rat adenohypophysis in v

Electrical Properties of Cells in the Adenohypophysis -An in vivo Study

Measurements of transmembrane potential, membrane resistance, and membrane capacitance in cells of the rat adenohypophysis show these parameters to be significantly lower than those for neuronal cells. The examination of a relatively pure population of ‘hypersecreting’ thyrotrophic cells, produced by the chronic adminstration of propylthiouracil, resulted in a significant change in the mean amplitude of the transmembrane potential, but no significant changes in the other membrane electrical parameters.