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Biomedical subjects

I Assenmacher

Publications and source records attributed to I Assenmacher.

At least 73 records · Page 4Linked to original sources
PubMed1985

[Submaxillary glands in an endocrine context].

The evidence for interrelationships between the submandibular salivary glands (SMG) and the endocrine system is reviewed. Firstly, it has been clearly demonstrated that various hormones participate in the molecular control of exocrine enzyme synthesis in the SMG, and more particularly within the cells of the convoluted granular tubules of the gland. Testosterone was thus shown to stimulate the synthesis of a series of SMG enzymes via its specific cellular receptors and the genetic machinery of protein synthesis, while the active thyroid hormone T3, together with the glucocorticosteroids act synergistically with testosterone. In addition, experimental evidence is accumulating, ascribing to the SMG an endocrine function. More specifically, two important hormonal factors appear to originate in the SMG: the nerve growth factor (NGF), a polypeptide of 140.000 d which is highly concentrated in the SMG and plays a major role in the ontogenetic development and in the functions of spinal and sympathetic ganglia; and the epidermal growth factor (EGF), a 6.045 d peptide displaying a variety of biological actions including promotion of epidermal development, eruption of the incisors, stimulation of pituitary secretion of ACTH and GH, and inhibition of gastric and of thyroid hormone secretion. As previously observed for the SMG exocrine enzymes production, the two endocrine secretions of the SMG are also controlled by various classical hormones such as testosterone, thyroid hormones and adrenocorticosteroids. Finally, a more complex regulatory loop involving the SMG hormones was recently described, including a retrograde axonal transport of NGF from the SMG to the superior cervical ganglion (SCG) where it participates in transmitter syntheses, and, beyond the SCG, in the control of various targets of the SCG such as the pineal gland and other neuroendocrine regulations. Summing up, the buccal segment presently appears as a mixed glandular section with both exocrine and endocrine functions in the same line as the lower segments of the digestive tract, i.e. stomach, duodenum, liver and pancreas.

Adrenal Cortex Hormones↗
PubMed1985

[Demonstration of prolactin flow into the cerebrospinal fluid of the alert rat in a pulsatile circhoral manner by push-pull cannulation of the 3d ventricle].

In 8 male unanesthetized rats, sequential sampling of cerebrospinal fluid (CSF) from a push-pull cannula implanted into the 3rd ventricle revealed that prolactin was present in this fluid, where it displayed circhoral pulsatility resembling the temporal variations in plasma prolactin observed in the same animals. Although basal prolactin levels were lower in the CSF than in the plasma, the amplitude of the circhoral prolactin pulses was twice as great in the CSF as in the plasma compartment. The possible origin and role of CSF prolactin are discussed.

Animals↗
PubMed1984

In vivo release of somatostatin from rat median eminence after local K+ infusion or delivery of nociceptive stress.

The effects of local infusion of a 16 mM K+ solution or of a nociceptive stress on the release of somatostatin (SRIF) from the hypothalamus was measured in unanesthetized male rats implanted with a push-pull cannula in the median eminence. Although the baseline secretion rate of SRIF was increased in animals displaying agitation as a result of handling stress, both treatments induced fast doubling of SRIF release lasting for 15-30 min. Neither an equimolar Na+ infusion into the median eminence nor a similar K+ infusion into the 3rd ventricle had any affect on this release. The possible role of SRIF release in the mechanism of growth hormone inhibition following nociceptive stress is discussed.

Animals↗
PubMed1984

Ultrastructural analysis of the noradrenergic innervation of rat supraoptic nucleus.

The noradrenergic innervation of the rat supraoptic nucleus (SON) was examined by high resolution radioautography after animals had been intracerebrally injected with [3H]noradrenaline (NA). In the medial portion of the SON, noradrenergic varicosities were scattered throughout this nucleus, but were preferentially concentrated in its ventral subdivision. 25.5% of these NA varicosities displayed typical synaptic contacts, with either the somatic or proximal dendritic portions of neurosecretory neurons (9.2%) or with small dendritic processes of such neurons (16.3%). The possibility is discussed that at least some of the dendritic NA synapses detected in the ventral subdivision of the SON, which preferentially contains vasopressinergic perikarya, may affect the neurosecretory neurons located in the dorsal part of this nucleus, which preferentially contains oxytocinergic perikarya.

Animals↗
PubMed1984

Diurnal variations in estradiol binding site concentrations in the hypothalamus, pituitary and uterus of prepuberal rats.

Available cytosolic estradiol binding sites (EBS) were estimated at 6 h intervals over a 24 h period in individual extracts of uteri, pituitaries and hypothalami from intact, ovariectomized or hypophysectomized 28-day old rats, maintained from birth in a 12 h light-12 h dark photoperiod. Plasma estrogen levels were also recorded, in intact rats, they displayed a 20% rise during daytime. In the uterus and pituitary of ovariectomized rats EBS concentrations exceeded by one third those of intact controls. In intact animals, significant diurnal variations in EBS were observed in both these tissues, with increased daytime levels. These variations appeared to depend on the amount of estrogen in the plasma, as they were not observed in spayed rats. No diurnal variations in EBS were apparent in the hypothalamus of intact animals, but they did occur in ovariectomized rats, and even more significantly in hypophysectomized rats, although the latter had lower EBS concentrations than spayed animals. These variations were presumed to result from the interference of pituitary-controlled hormones other than estrogens in the regulation of EBS levels.

Animals↗
PubMed1984

Androgen control of transcortin binding capacity in adult male ducks.

In adult male ducks submitted to marked variations in plasma testosterone concentration, plasma transcortin (CBG) levels were shown to be closely related to the level of plasma testosterone. In connection with previous data on female ducks, the results strongly support the evidence that at least in this species, CBG is under a stimulatory control by testosterone.

Animals↗
PubMed1984

External factors controlling annual testosterone and thyroxine cycles in the edible dormouse Glis glis.

Annual patterns of hibernation, body weight, plasma testosterone and thyroxine were measured in two groups of edible dormice exposed to a constant photoperiod and to either environmental temperature (I), the four functions displayed annual cycles and the two hormonal cycles were parallel and restricted to the aroused state, while in group II only irregular infradian fluctuations were observed. However, a body temperature of 30 degrees C remained the critical lower limit enabling the start of the testosterone cycles for the two groups. Respective roles of endogenous and synchronizing mechanisms in controlling biological rhythms are discussed.

Animals↗
PubMed1983

Acute and delayed effects of picrotoxin on the adrenocorticotropic system of rats.

To investigate the possible effect of GABA on the corticotropic system, the potent GABA antagonist picrotoxin was injected into two groups of 14 female rats at 07.00 h and 19.00 h, respectively. A single subconvulsive I.p. injection dramatically raised plasma ACTH and corticosterone, and thereafter suppressed the circadian rhythm of ACTH, but not of corticosterone, for 24 h in the group injected at 07.00 h and for 48 h in the one injected at 19.00 h and increased mean hormonal levels. Results are discussed in the light of the possibility that inhibition by the GABAergic system and stimulation by the serotoninergic system might be components of the mechanism controlling the circadian rhythm of ACTH.

Adrenocorticotropic Hormone↗
PubMed1983

[Demonstration of pulsatile secretion of somatostatin in the third cerebral ventricle of unanesthetized rats].

Using a specially designed push-pull cannula stereotaxically implanted into the 3rd ventricle, a pulsatile secretion of IR-SRIF with a circhoral periodicity was detected in male rats. At 30 min. to 1 h 1/2 intervals the secretion rate of the neuropeptide rose from a baseline rate of 14.5 +/- 0.5 pg/10 min., corresponding to a baseline concentration of 60 +/- 2 pg/ml to peaks of 50 +/- 5 pg/10 min. or 210 +/- 22 pg/ml, respectively. This pulsatile pattern was restricted to rats where histological examination showed no dilation pictures of the ventricle. The possible origin and function of intra-ventricular IR-SRIF are discussed.

Animals↗
PubMed1983

Retrograde axoplasmic transport of neurosecretory material. An immunocytochemical and electron-microscopic study of transected axons in normal and colchicine-treated rats.

The axonal transport of neurosecretory material was studied in neurosecretory axons of the supraoptico-posthypophyseal system after in-situ transection of the median eminence. Two hours, 8 h, and 18 h after the lesion, both vasopressin and oxytocin antibodies revealed progressive accumulations of immunoreactive material not only in the proximal but also in the distal stumps of the transected axons. The electron-microscopic examination of these axonal portions revealed that such intense immunopositive labelings could be correlated, in both stumps, to a conspicuous accumulation of neurosecretory granules. It is concluded that, under normal physiological conditions, a significant amount of axoplasmic neurosecretory material is transported in retrograde direction and that such a retrograde transport mainly involves neurosecretory granules.

Animals↗
PubMed1983

Annual plasma testosterone and thyroxine cycles in relation to hibernation in the edible dormouse Glis glis.

Twelve male edible dormice, captured in the autumn of 1979, were studied for 2 years under natural lighting in an animal enclosure with permanently open windows, at Montpellier, in Southern France (latitude 43 degrees 50' N). Ambient temperature fluctuated annually between +4 and 27 degrees, and the photoperiod between 10L:14D and 16L:8D. Another group of 26 animals, captured in the autumn of 1980, was observed under the same conditions for 1 year. Body weight and plasma testosterone and thyroxine concentrations were measured at monthly intervals under standardized conditions. Hibernation generally extended from October to February but lasted till May in a few cases, and the critical temperature for dormancy varied between 13 and 16 degrees in November and 23 degrees in May. Body weight fluctuated annually according to a biphasic pattern, with two maxima, respectively, in spring and autumn (prehibernation), and two minima, in summer and winter. However, plasma testosterone and thyroxine concentrations displayed clearly monophasic annual cycles, closely correlated, both to each other and to the ambient temperature and photoperiod. Both the testosterone and thyroxine cycles culminated in June-July. Interestingly, the annual ascending phase for both hormonal cycles never preceded the terminal arousal of the animal. Further, whatever the season, 30 degrees was clearly the critical minimal body temperature required for a seasonal increase to occur in plasma testosterone. These annual cycles are discussed in the light of the data acquired recently for hibernators other than the dormouse.

Animals↗
PubMed1983

CNS control of the circadian adrenocortical rhythm.

The effects of various CNS impairments on the circadian rhythm of plasma ACTH and Corticosterone (C) were studied in individual cannulated female Sprague-Dawley rats. Pinealectomy had no effect whatever the light perception (intact or blinded rats). Bilateral ablation of paraventricular nuclei did not obliterate the hormonal rhythms, although the rhythms' amplitude were markedly depressed. On the other hand, destruction of suprachiasmatic nuclei (SCN) or systemic blockade of the serotoninergic (5-HT) system by pCPA blocked ACTH rhythm at baseline levels, although circadian or ultradian fluctuations with normal amplitudes persisted for C. Similar effect was observed in several blinded rats with raphe lesions suppressing 5-HT innervation of SCN. Daily 5-HTP injections, if given 4 h after dawn restored normal ACTH rhythm. The respective role of related structures in the rhythms' control will be discussed.

Adrenal Cortex↗
PubMed1983

Direct evidence of short-term cold-induced TRH release in the median eminence of unanesthetized rats.

IR-TRH release in the median eminence was directly estimated in conscious rats during the first 130 min of exposure to cold (4 degrees C), using a push-pull cannulation. A three-fold increase in IR-TRH release was observed, with a peak of 10.00 +/- 2.19 pg/15 min occurring 40 min after exposure to cold; control rats, left at 24 degrees C, stayed at the baseline secretion rate of 3.40 pg/15 min which was the sensitivity limit of the RIA assay.

Animals↗
PubMed1983

[Persistance of phase-coupling between the circadian rhythms of hypophyseal hormones in free-running rats].

The circadian rhythms in plasma ACTH, TSH, LH and PRL were explored in sighted or blind, spayed and estrogen-implanted rats. A marked endogenous circadian rhythmicity was shown to persist in the blind animals for the 4 endocrine rhythms. The endogenous rhythms also kept very close reciprocal phase relationship as in the synchronized state, and they were peaking almost simultaneously, after 60 d. of free-running. Finally the endogenous hormonal rhythm maintained their usual phase relationships with the endogenous activity rhythm, so that the circadian phase of increased hormonal secretion coincided with the circadian resting phase of the sleep/wake rhythm. These results are discussed in the light of the alternate theory of one vs multiple but phase-locked circadian pacemakers driving endocrine and behavioral circadian rhythms.

Adrenocorticotropic Hormone↗
PubMed1983

[Persistence of circadian rhythms of plasma ACTH and corticosterone after pinealectomy in sighted or blind rats].

The possible effects of pinealectomy on the corticotropic system was studied in either sighted or ocular enucleated adult female Rats. Individual ACTH and corticosterone measurements were performed on sequential plasma samples obtained over a 48 hrs period from a carotid implanted cannula. Compared with their respective sighted or blind controls, pinealectomized Rats displayed no alteration in the hormonal rhythms' periodicity, phase, mean level and amplitude. On the other hand, ocular enucleation, whether or not associated with pinealectomy depressed the amplitude and to a lesser extent the mean level of the ACTH rhythm, and paradoxically increased the corticosterone rhythm's mean level. While no pineal factors appear therefore required for a normal corticotropic rhythmicity, the possible regulating role of retinal melatonin may be discussed.

Adrenocorticotropic Hormone↗
PubMed1983

[Extrahypothalamic efferent pathways of the suprachiasmatic nucleus in the rat].

Efferent connections of the suprachiasmatic nucleus (SCN) in the Rat were evidenced using specific silver impregnation techniques designed to explore degenerating nerve fibers and terminals after a unilateral destruction of the suprachiasmatic nucleus. Suprachiasmatic efferences were confirmed and terminal buttons were identified in the septum, habenula and paraventricular nucleus of the thalamus. In addition suprachiasmatic fibers and nerve endings were revealed in the medial, cortical and central nuclei of the amygdala in the hippocampic subiculum, in different areas of the olfactory system and in the area parolfactoria.

Animals↗
PubMed1982

Interrelations between binding affinity and metabolic clearance rate for the main corticosteroids in the rabbit.

In the rabbit, the metabolic clearance rate (MCR) was found to be higher for corticosterone than for cortisol. At the same time corticosterone, aldosterone and 11-dehydrocorticosterone showed similar MCR while cortisone ranged at intermediate levels between cortisol and corticosterone. The relative binding affinity of transcortin to the corticosteroids, as calculated by an in vitro technique, decreased progressively from cortisol, to cortisone, then to corticosterone, then 11-dehydrocorticosterone and, finally to aldosterone. The occurrence of antibodies in plasma, induced against aldosterone, corticosterone or even cortisone resulted in a marked decrease in the MCR of the corresponding steroid, to the level measured in controls for cortisol. We deduced that, in rabbits: (1) the MCR of a corticosteroid is clearly connected with its binding to a specific protein; (2) in spite of the relatively high binding affinity of transcortin for corticosterone as compared to other species it nevertheless appears unable to significantly protect the steroid against peripheral metabolism; (3) a very effective protection is however, induced, by raising a specific antibody with a high binding affinity for corticosterone.

Adrenal Cortex Hormones↗