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Biomedical subjects

C Denef

Publications and source records attributed to C Denef.

At least 91 records · Page 5Linked to original sources
PubMed1985

Stimulation of growth hormone release by vasoactive intestinal peptide and peptide PHI in rat anterior pituitary reaggregates. Permissive action of a glucocorticoid and inhibition by thyrotropin-releasing hormone.

In superfused rat anterior pituitary cell reaggregates, cultured for 5 days in serum-free defined medium, vasoactive intestinal peptide (VIP) concentration-dependently stimulated prolactin (Prl) release but had only a marginal effect on growth hormone (GH) release. When reaggregates were cultured in the presence of 80 nM dexamethasone (Dex) VIP strongly stimulated GH release from a concentration as low as 0.1 nM. VIP did not stimulate LH release. Peptide PHI also stimulated GH release but thyrotropin-releasing hormone (TRH) or angiotensin II did not. In fact, TRH slightly but transiently inhibited basal GH release and strongly inhibited VIP-stimulated GH release. GH-releasing factor (GRF) stimulated GH more potently and with higher intrinsic activity than VIP but GRF did not increase Prl release. The present data indicate that under defined hormonal conditions VIP and PHI are capable of stimulating GH release and that TRH can antagonize this effect by a direct action on the pituitary.

Animals↗
PubMed1985

Regulation of prolactin release by angiotensin.

In superfused anterior pituitary cell aggregates, prolactin release is stimulated by angiotensin II (AII) in a concentration-dependent fashion between 0.1 and 10 nM. When studied in aggregates prepared from pituitary cell populations separated according to size by unit gravity sedimentation, the PRL response to AII was weak in a population enriched in lactotrophs but deprived of gonadotrophs. In other separated populations, the response increased with the proportional number of gonadotrophs. The response also increased when lactotrophs were co-aggregated with an enriched population of gonadotrophs. It is proposed that the PRL response to AII is augmented by an intercellular messenger system presumably operating between gonadotrophs and lactotrophs.

Angiotensin II↗
PubMed1984

Stimulation of spontaneous and dopamine-inhibited prolactin release from anterior pituitary reaggregate cell cultures by angiotensin peptides.

In superfused anterior pituitary reaggregate cell cultures angiotensin II (AII) stimulated both spontaneous and dopamine-inhibited prolactin (PRL) release from subnanomolar concentrations. Angiotensin I (AI) and angiotensin III (AIII) also stimulated PRL release. The magnitude and rate of response to AI was equal to or only slightly lower than that to AII. However, the angiotensin converting enzyme (ACE) inhibitors captopril and teprotide (1 microM) completely abolished the PRL response to 0.1 nM AI and strongly reduced that to 1 nM AI. The intrinsic activity of AIII was lower than that of AII but could be enhanced by adding 2 microM of the aminopeptidase inhibitor amastatin to the superfusion medium. After withdrawal of AIII, PRL secretion rate rapidly returned to baseline levels, whereas after withdrawal of AI or AII, secretion fell to a level remaining significantly higher than basal release. The present findings indicate that stimulation of PRL release by AI is weak unless it is converted into AII by ACE and that aminopeptidase may be important in determining the magnitude and termination of the PRL response. Furthermore, the active peptides induce a different pattern of response.

Angiotensin I↗
PubMed1984

Beta 2-receptors in the rat anterior pituitary mediate adrenergic stimulation of prolactin release.

As previously shown, the beta-adrenergic agonists isoproterenol, epinephrine and norepinephrine stimulate prolactin (PRL) release from superfused rat anterior pituitary cell aggregates. In order to further characterize the beta-adrenergic response in this tissue preparation, the effects of various beta-adrenergic agents were investigated. The beta 2-agonist, zinterol, stimulated PRL release at concentrations more than 4 orders of magnitude lower than prenalterol, a beta 1-agonist with high potency in rat heart. The order of potency of the antagonists IPS 339 (beta 2), ICI 118.551 (beta 2), propranolol, sotalol, practolol (beta 1), metoprolol (beta 1) and H 35/25 for inhibition of beta-agonist-stimulated PRL release provided additional support for a beta 2-stimulatory effect. beta-Agonists were also capable of stimulating PRL release from superfused intact pituitaries. The beta-adrenergic response desensitized rapidly during prolonged exposure of the aggregates to beta-agonists.

Adrenergic beta-Agonists↗
PubMed1984

Influence of corticosteroids on prolactin release from anterior pituitary cell aggregates cultured in serum-free medium. Differential effects on dopamine-induced inhibition, post-dopamine rebound and stimulation by TRH, vasoactive intestinal peptide (VIP), angiotensin II and isoproterenol.

Dispersed rat anterior pituitary cells were allowed to reassociate into spherical aggregates by gyrotory shaking in serum-free chemically defined culture medium. When aggregates were superfused after being cultured for 5 days in this medium, stimulation of PRL release by TRH, VIP, angiotensin II and the beta-adrenergic agonist isoproterenol was comparable to that of aggregates cultured in serum-supplemented culture medium. Addition to the serum-free medium of 80 nM dexamethasone (Dex) resulted in a significant enhancement of the stimulation of PRL release by TRH, VIP and angiotensin II but not of the stimulation of PRL release by isoproterenol. Dex also failed to influence the inhibition of PRL release by 10 min exposure to 10 nM dopamine (DA). However, Dex significantly enhanced the post-DA rebound secretion of PRL. After 3 weeks in culture Dex provoked a similar potentiation of the response to angiotensin as at 5 days in culture but it abolished almost completely the stimulatory effect of isoproterenol. It is concluded that pituitary cell aggregates cultured in defined serum-free medium are a reliable system to study the multifactorial control of PRL release. The data show that peptidergic, dopaminergic and beta-adrenergic control at the pituitary level is differentially modulated by corticosteroids.

Adrenal Cortex Hormones↗
PubMed1984

Stimulation of prolactin secretion after short term or pulsatile exposure to dopamine in superfused anterior pituitary cell aggregates.

The dynamics of dopamine (DA) action on PRL release was studied in superfused rat anterior pituitary cell aggregates, cultured for for 5 days either in conventional or in serum-free defined medium. In aggregates cultured in conventional medium 0.1-1 nM DA applied for 20 min provoked a rapid and concentration-dependent inhibition of PRL release, lasting only a few minutes, after which there was a gradual rise in secretion up to near baseline levels. A sustained inhibition was obtained from DA concentrations more than or equal to 10 nM. When DA, used at the latter concentration, was withdrawn from the superfusion medium, a marked rebound secretion of PRL occurred, exceeding basal release for as long as 40-50 min. Rebound secretion was not followed by a compensatory fall in secretion rate. After a 10-min pulse of 10 or 30 nM DA, the amount of PRL released above baseline was considerably higher than the amount of PRL not released during the time DA was present. The latter stimulation of PRL release was not seen after a 40- or 90-min exposure time to DA. However, when DA was given for 40 min in 10 pulses of 4 min (4 min DA on 4 min DA off), a clear-cut stimulation of PRL release followed the termination of the pulses. When the serum used in the culture medium was extracted with dextran-coated charcoal, post-DA rebound secretion of PRL was markedly diminished. The latter secretion pattern partially reappeared when the extracted serum was supplemented with 10 nM dexamethasone. DA had similar effects on PRL release in aggregates cultured in serum-free defined medium. Dexamethasone did not affect DA-inhibition but strongly stimulated post-DA rebound, and this effect was potentiated by T3 present in the defined medium. There was three to four times more PRL secreted in excess of basal release than was inhibited during exposure to DA. The present data suggest a dual action of DA on PRL release: inhibition during tonic exposure to the catecholamine and inhibition-mediated stimulation after pulsatile exposure.

Animals↗
PubMed1983

Stimulation of prolactin release by angiotensin II in superfused rat anterior pituitary cell aggregates.

Superfusion of rat anterior pituitary cell aggregates with 10-min pulses of 0.1-10 nM angiotensin II (AII) resulted in a prompt and concentration-dependent rise of PRL release. The effect could be blocked by saralasin, an AII receptor antagonist. The response to AII, but not that to TRH, was rapidly desensitized: a 10 nM AII pulse caused an 80% depression of the response to a subsequent 10 nM pulse given 50 min later. The data provide a possible functional significance for the renin-angiotensin system recently demonstrated in the anterior pituitary.

Angiotensin II↗
PubMed1983

Electrophysiological properties of normal somatotrophs in culture. An intracellular study.

Normal rat pituitary cells were isolated and enriched to obtain a relatively pure population of growth hormone (GH) secreting cells by sedimentation at unit gravity and subsequently grown in culture. The electrophysiological properties of these cells were studied with intracellular recording techniques. 4-6-day-old cells did not show active electrical properties. At 7-9 days the cells were able to generate evoked responses (fast responses) which were blocked by inhibitors of calcium flux and prolonged with tetraethylammonium. The resting potential of these cells was sensitive to external local application of substances known to act on the release of GH. External elevated K+ induced a strong depolarizing response which was associated with an increase of membrane conductance. Somatostatin induced a hyperpolarizing response associated with a decrease of membrane conductance. It is suggested that the fast Ca2+-dependent responses and the slow variations of the resting potential induced by substances which modify hormone release may play an important role in the control of the secretory process of the presumably GH-secreting cells.

Animals↗
PubMed1983

Evidence for paracrine interaction between gonadotrophs and lactotrophs in pituitary cell aggregates.

Pituitary cell aggregates prepared from 14-day-old male or female rats and maintained for 4-5 days in culture were superfused with LHRH during periods of 20 or 90 min. LHRH provoked a rapid and sustained rise of PRL release at concentrations similar to those stimulating LH release (10(-11)-10(-8) M). Dopamine, at a concentration inhibiting PRL release for 90%, weakened but did not prevent this stimulation. LHRH also stimulated PRL release in aggregates prepared from adult male rat pituitary cells, but the effect was weaker and seen only after a more prolonged period in culture. There was no PRL response to LHRH in aggregates of lactotroph-enriched populations, obtained by gradient sedimentation at unit gravity, in which only few and small gonadotrophs are present. When a lactotroph-enriched/gonadotroph-poor population was coaggregated with a highly enriched population of large gonadotrophs, LHRH very effectively stimulated PRL release, the extent of stimulation being dependent on the proportional number of gonadotrophs in the coculture. Superfusion of lactotroph-enriched/gonadotroph-poor aggregates with medium in which the gonadotroph-enriched aggregates had previously been incubated for 3 h with 1 nM LHRH (gonadotroph-conditioned medium) also provoked a clear-cut rise in PRL release. This effect was not due to LH, FSH, or the small amounts of PRL present in the gonadotroph-conditioned medium. The LHRH antagonist [D-Phe2-D-Ala6]LHRH was capable of blocking the PRL response to LHRH but not that to the gonadotroph-conditioned medium. In the lactotroph-gonadotroph coaggregates TRH stimulated PRL release but had no effect on LH release. TRH was also ineffective in releasing LH or FSH in populations containing both gonadotrophs and thyrotrophs. The present data suggest that gonadotrophs can activate the secretory activity of the lacotrophs through the release of a paracrine humoral factor.

Animals↗
PubMed1983

5 alpha-dihydrotestosterone formation and its functional significance in rat anterior pituitary, subpopulations of gonadotrophs and cell cultures.

The present paper reviews the work in the author's laboratory on the conversion of testosterone to 5 alpha-reduced metabolities and its regulatory control in intact pituitary, in enzymatically dispersed pituitary cells and in enriched populations of gonadotrophs isolated by unit gravity sedimentation. The data show that 5 alpha-reductase is located mainly in gonadotrophs and the possible physiological significance is discussed. A new culture method, suitable to study the regulation of 5 alpha-reductase and its biological significance in vitro, is presented.

Aging↗
PubMed1982

Ultrastructural and functional characteristics of rat pituitary cell aggregates.

Suspensions of isolated rat pituitary cells and gonadotroph- or lactotroph/somatotroph-enriched subpopulations obtained by unit gravity sedimentation were allowed to aggregate by constant gyrotory shaking, yielding aggregates of 100-150 micrometers. Within a few days, the aggregated pituitary cells became organized in a tissue-like configuration. There was no proliferation of mesenchymal cells. Glandular cells had a round to oval shape and formed specialized cell junctions. Areas of close apposition alternated with more dilated intercellular spaces. The different pituitary cell types retained their characteristic ultrastructural features and secretory granules, typical of the various cell types. Functional characteristics could be accurately studied in a superfusion system. LH, FSH, and PRL secretion showed very rapid on-off responses to nanomolar concentrations of the specific regulatory stimuli LHRH, TRH, vasoactive intestinal peptide, and dopamine. Aggregates remained highly responsive to LHRH even after 3 weeks in culture. The results indicate that isolated pituitary cells allowed to reaggregate in suspension culture form viable and functional multicellular structures which have maintained in vivo characteristics.

Animals↗
PubMed1982

Beta-adrenergic stimulation of prolactin release from superfused pituitary cell aggregates.

l-Isoproterenol (l-ISO), a specific agonist of beta-adrenergic receptors, evoked a prompt rise of prolactin (PRL) release from superfused anterior pituitary cell aggregates established in culture for 5 days. The effect was concentration-dependent between 1 and 100 nM. d-Isoproterenol was more than 2 orders of magnitude weaker than the l-isomer. When dopamine receptors were blocked with domperidone, PRL secretion was also stimulated by l-epinephrine (E) and l-norepinephrine (NE), the rank order of potency being l-ISO greater than E much greater than NE. Under the latter conditions dopamine and the alpha-adrenergic agonists, clonidine and phenylephrine, had no stimulatory effect at 1 microM. Stimulation of PRL release by l-ISO and E was blocked by the beta-receptor antagonist, propranolol, but not by the alpha-receptor blocker, prazosin.

Animals↗