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Biomedical subjects

K M Knigge

Publications and source records attributed to K M Knigge.

At least 55 records · Page 3Linked to original sources
PubMed1979

Characterization of an in vitro method for demonstrating thyrotropin-releasing hormone-stimulated prolactin secretion.

Anterior pituitaries of normal adult male rats were subjected to synthetic thyrotropin-releasing hormone (TRH) treatment in an acute incubation system which employed pretreatment of the glands with plasma obtained from the donor animals. Following a 60-min preincubation period in a 1:1 mixture of Krebs-Ringer bicarbonate buffer (KRB) and plasma, media and hemipituitary prolactin (PRL) concentrations were significantly (p less than 0.01) increased after a 40-min treatment with 500 pg TRH. The TRH effect was absent among hemipituitaries preincubated in KRB alone. Plasma obtained from older donors was more potent than was plasma from younger rats in this effect. TSH secretion was markedly increased by 500 pg TRH, whether or not plasma preincubation was employed. A dose response of PRL release to concentrations of TRH from 100 pg to 6.0 ng was observed. Crude extracts of median eminence also effected enhanced PRL release using the plasma preincubation technique. The results suggest that plasma preincubation of explanted pituitaries increases PRL cell sensitivity to TRH, perhaps by enzymatic inactivation of endogenous TRH bound to cellular membrane receptors.

Aging↗
PubMed1979

In vitro release of prolactin by thyrotropin-releasing hormone: influence of dopamine, thyroxine, and cycloheximide.

An acute incubation procedure, using explanted normal rat hemipituitaries pretreated with fresh plasma obtained from pituitary donor animals, was employed to further investigate the in vitro stimulation of prolactin (PRL release by thyrotropin-releasing hormone (TRH). Pretreatment with dopamine (0.1 microgram/ml) caused a 30-50% decrease in the amount of PRL released into incubation media; the inhibitory effect of dopamine was not reversed by treatment with 0.5-6.0 ng. TRH, although these TRH concentrations consistently stimulated PRL release from pituitaries not exposed to dopamine. Treatment with thyroxine (10(-6) to 10(-5) M) showed a competitive inhibition of thyrotropin release by TRH (0.5 ng), but was without effect on TRH-stimulated PRL release. Cycloheximide (100 microgram/ml) blocked a net increase in PRL levels. TRH, nevertheless, significantly increased PRL release in the presence of cycloheximide. The results indicate that neither dopamine nor thyroxine compete with TRH in causing PRL release, and that the TRH stimulation of PRL release is unrelated to ongoing levels of hormone synthesis.

Animals↗
PubMed1978

Primary cultures of dispersed cells of rat pineal gland. I. Fine structure and indole metabolism.

In vitro indole metabolism and ultrastructural morphology of the pineal gland of male rats were examined. A comparison of the effect of norepinephrine stimulation on indole synthesis in whole cultured glands and preparations of dispersed pineal cells is discussed. Our studies on the performance of dispersed cells during the first 24 h after preparation indicate a strong dependence of pineal cells upon physical attachment to the culture dish and probably also on cell-to-cell contact.

Animals↗
PubMed1978

Serum levels of prolactin, LH and LH-RH after ablation of the medial basal hypothalamus.

4 weeks after surgical ablation (MHA) of the medial basal hypothalamus (MBH) in adult male rats, serum levels of prolactin, LH, and LH-RH were determined by radioimmunoassay. Blood samples were obtained by jugular venipuncture under ether anesthesia (designated 'stress' samples) and 30 min after the ether stress by rapid decapitation (designated 'resting samples). 30 min after ether, serum levels of prolactin, LH, and LH-RH in MHA rats were comparable to those of intact and sham-operated controls. Among intact and sham-operated rats, ether elicited an initial increased in prolactin but not in LH or LH-RH. In the MHA group, prolactin levels were also acutely increased, although the increment was not as great as in control groups. The data indicate that considerable basal prolactin and LH secretion persists after MHA, and that this continued secretion may be regulated by neurohoromones such as LH-RH which arise from areas outside the MBH.

Animals↗
PubMed1977

Identification of catecholamine and luteinizing hormone-releasing hormone (LHRH)-containing neurons in primary cultures of dispersed cells of the basal hypothalamus.

Primary cultures of dispersed cells were prepared from 3-5 mg pieces of basal hypothalami of 10-12-day-old rats. The tissue included median eminence, arcuate nucleus and variable amounts of adjacent hypothalamus and preoptic area. The dispersion procedure consisted basically of tissue trypsinization and mechanical dissociation of cells. They were cultured in a modified L-15 medium in an air atmosphere. Neurons survived approximately 3 months. On the basis of morphological characteristics, two basic cell types could be distinguished. One was a larger (50 mum diameter) multipolar cell; microspectrofluorometric analysis revealed that a small percentage of these neurons contained a catecholamine. A second type was smaller, fusiform or ovoid and generally bipolar; a significant number of these were immunoreactive for the releasing hormone LHRH.

Animals↗
PubMed1977

Osmotic control of vasopressin release by rat hypothalamo-neurohypophyseal explants in organ culture.

The rat hypothalamo-neurohypophyseal system (HNS) in organ culture has been used as an in vitro system for studying the osmotic control of vasopressin (VP) release. The HNS retains osmotically sensitive components as demonstrated by changes in the rate of VP release following alterations in the osmolality of the culture medium. Increasing the osmolality from 295 to 305 mosmol/kg H2O by the addition of NaCl resulted in a 2.5-fold increase in VP release. VP release was significantly decreased subsequent to reducing the osmolality from 295 to 280 mosmol/kg H2O by the addition of distilled water. Also, VP release was stimulated when the osmolality was increased to 300 mosmol/kg H2O by the addition of mannitol, but not by additions of urea or glucose which resulted in comparable increases in the tonicity of the culture medium. These studies demonstrate that the HNS in organ culture responds appropriately to osmotic challenges within the physiological range, and support Verney's concept of an osmoreceptor inasmuch as both NaCl and mannitol were effective osmotic agents.

Animals↗
PubMed1976

Fine structure of neurons of the arcuate nucleus and median eminence of the hypothalamus of the golden hamster following immobilization.

The fine structure of arcuate neurons of the arcuate nucleus, the ependymal tanycytes and the contact zone of the median eminence was examined following immobilization, an acute stress which significantly activated the hypothalamo-pituitary-adrenal (HPA) axis. Arcuate neurons of immobilized adult male hamsters displayed morphological indications of heightened activity; the number of lysosomes and dense core vesicles (80-120nm) was increased. A markedly greater number of dense core vesicles was present in axon terminals of the contact zone of the mid-central median eminence and the ventral proximal stalk. Tanycytes of the median eminence exhibited an augmented number of electron dense bodies in both perikarya and end processes. These results indicate that the arcuate neurons, the axons of the contact zone, and the ependymal tanycytes of the hamster medial basal hypothalamus (MBH) may be involved in the response to immobilization.

Animals↗
PubMed1976

Localization of dopamine in the endocrine hypothalamus of the rat.

Microspectrofluorometry, fluorescence histochemistry and light and electron microscopic autoradiography have established the presence of sub-populations of neurons in the arcuate-periventricular region of the rat hypothalamus that sequester both radiolabeled dopamine and demonstrate formaldehyde-induced fluorescence. These characteristics are consistent with a catecholaminergic function. Selective sequestration of 3H-dopamine at the light and ultrastructural level is discussed in the context of an ultrashort loop autoregulatory mechanism for this neuronal population.

Animals↗
PubMed1976

Monosodium glutamate induced lesions of the arcuate nucleus. I. Endocrine deficiency and ultrastructure of the median eminence.

Monosodium glutamate was administered daily on days 5 through 10 postnatally at a dose of 2.5 mg/gm body weight. Counts of remaining perikarya in the arcuate nucleus of adult mice indicated approximately an 80% decrease in the number of perikarya. The arcuate lesion resulted in endocrine deficits; reporductive capacity was reduced, animals were smaller in stature and obese, and the weights of the anterior pituitary, ovaries and testes were significantly decreased while adrenals were unaffected. Light microscopic studies revealed no significant changes in thickness or general histological appearance of the median eminence. At the electron microscope level, there were no alterations in the number of nerve terminals or dense core vesicles per unit area in the contact zone. These observations suggest that afferents to the median eminence from the arcuate nucleus may form a relatively small portion of its total nerve terminal population.

Afferent Pathways↗
PubMed1976

Monosodium glutamate induced lesions of the arcurate nucleus. II. Fluorescence histochemistry of catecholamines.

The effect of the monosodium glutamate (MSG) induced lesion of the arcuate nucleus on catecholamines in the arcuate nucleus and median eminence of the mouse hypothalamus was determined using the Falck-Hillarp histofluorescence technique. The number of fluorescent perikarya in the arcuate nucleus of treated animals was decreased approximately 60%; the fluorescence intensity of surviving neurons was notably reduced. These changes were accompanied by a reduction in the intensity of fluorescence in the median eminence. Pretreatment of control and MSG-lesioned animals with a monoamine oxidase inhibitor (pargyline) greatly increased fluroescence in the median eminence and arcuate nucleus of both groups. However, the number of fluorescing perikarya of the arcuate nucleus of the normal pargyline treated group far exceeded that of the pargyline MSG animals. It is concluded that neonatally administered MSG caused destruction of a large number of dopaminergic arcuate perikarya.

Animals↗
PubMed1976

The effects of pentobarbital and ether anesthesia on hypothalamic LH-RH in the rat.

The effects of ether and pentobarbital anesthesia on hypothalamic and cerebrospinal fluid (CSF) LH-RH content were studied in male rats. Ether elevated hypothalamic LH-RH 30 min after a 3-min exposure; pentobarbital (30 mg/kgital (30mg/kg) caused no change. The ether-induced increase in LH-RH content was not affected by pretreatment with pentobarbital; however, the increase was abolished in animals subjected to hypothalamic deafferentation. Changes in CSF LH-RH generally paralleled the hypothalamic changes; ether, for example, elicited a significant rise. These results demonstrate the complex hypothalamo-pituitary-CSF interactions which occur in response to general anesthetics.

Animals↗
PubMed1976

TRH-degrading enzyme activity in peripheral and pituitary-portal plasma of the rat.

The enzymatic degradation of TRH was measured in peripheral and pituitary-portal plasma. Enzyme activity in peripheral plasma was 3.20 pg/min/mug plasma protein; in pituitary-portal plasma the rate of degradation was only 0.83 pg/min/mug protein. After dialysis, which removed virtually all endogenous TRH and LHRH, enzyme activity in peripheral and portal plasma was 2.24 and 0.60 pg/min/mug respectively. These data suggest that portal plasma contains large concentrations of unidentified substances which are competitive inhibitors or substrates for the enzyme or that portal plasma contains less TRH-degrading enzyme.

Animals↗