Biomedical subjects

F Mallo

Publications and source records attributed to F Mallo.

4 recordsLinked to original sources

PubMed1992

Effect of retinoic acid deficiency on in vivo and in vitro GH responses to GHRH in male rats.

Retinoic acid has recently been shown to increase growth hormone (GH)-gene transcription rate and GH synthesis in vitro. To investigate the role retinoic acid plays in the neuroregulation of GH secretion we have studied GH responses to growth hormone-releasing hormone (GHRH) in retinoic acid-deficient rats. Compared to normally fed male rats, retinoic acid-deficient rats showed a marked impairment in body weight, which was statistically significant after 3 weeks and maximal after 5-6 weeks (p less than 0.001). Yet, in vivo GH responses to different doses of GHRH (1, 5 and 25 micrograms/kg) in pentobarbital-anesthesized rats were similar in both groups. Also, in vitro GH responses to GHRH, forskolin, and KCl were similar in perfused pituitary cells taken from control and retinoic acid-deficient rats. However, further studies carried out in freely-moving rats showed the typical GH secretory pattern usually found in male rats of the control group, while retinoic acid-deficient rats displayed a highly variable GH secretory pattern with GH peaks of much lower amplitude. Finally, after gel electrophoresis of in vitro 35S-labelled proteins, no differences were observed in the molecular forms of GH. Considering these findings on normal pituitary responsiveness and alterations in GH pulsatility, our data suggest that retinoic acid deficiency leads to an alteration in the neuroregulation of GH secretion at the central level.

Animals↗

PubMed1991

Evidence for a direct pituitary inhibition by free fatty acids of in vivo growth hormone responses to growth hormone-releasing hormone in the rat.

The aim of this study was to determinate whether elevations in circulating free fatty acids (FFA) inhibit in vivo growth hormone (GH) responses to GH-releasing hormone (GHRH) by increasing hypothalamic somatostatin release or by acting directly on the pituitary. Thus, we have studied the effect of an Intralipid-heparin infusion on in vivo GH responses to GHRH in normal rats, normal rats passively immunized with antisomatostatin antiserum, rats with medial hypothalamic ablation, and hypophysectomized rats bearing two hypophyses under the renal capsule. Administration of 1 ml of Intralipid (500 microliters at -30 min and 500 microliters at -25 min) plus heparin (50 IU at -15 min) induced a marked decrease in GH responses to both 1 and 5 micrograms/kg of GHRH (p less than 0.01 at 5, 10 and 15 min for GHRH alone vs. GHRH plus Intralipid). A similar degree of inhibition was obtained after the administration of antisomatostatin antiserum (750 microliters i.v. at -60 min) previous to a challenge with 5 micrograms/kg of GHRH plus 1 ml of Intralipid (p less than 0.05 at 5 and 15 min, and p less than 0.01 at 10 min for GHRH plus normal rabbit serum vs. GHRH plus Intralipid plus antisomatostatin antiserum). Furthermore, administration of 1 ml of Intralipid also markedly reduced GH responses to GHRH in rats with medial hypothalamic ablation (p less than 0.01 at 5, 10, 15 and 30 min for GHRH alone vs. GHRH plus Intralipid) as well as in hypophysectomized rats bearing two hypophyses under the renal capsule (p less than 0.01 at 5, 10 and 15 min for GHRH alone vs. GHRH plus Intralipid).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Morphometry and classification of the cat hypothalamic capillaries using multivariate analysis.

Multivariate statistical methods were used to do morphological determination of the amount and the relation of the astrocytic foot processes (AF), astrocytic lamina (AL) and dense zones (DZ) on hypothalamic capillaries. We corroborated that 100% of the perivascular membrane is surrounded by glial astrocytic cytoplasm. Principal component analysis shows that the original variables are independent of one another. Cluster analysis confirms the individual situation obtained through the principal component analysis. Discriminant analysis shows that the discriminant capacity of the 3 variables is very significant. For the potential interrelations of astrocytic foot processes, astrocytic lamina and dense zones we have clearly differentiated four groups of hypothalamic capillaries.

Animals↗

PubMed1990

Estrogen-dependent effects of bombesin on in vivo growth hormone secretion in the rat.

Previous studies carried out in normal male or ovariectomized female rats have shown that bombesin plays an inhibitory role on growth hormone (GH) secretion. Since estrogens play an important role in the neuroregulation of GH secretion, we have studied the effects of bombesin on basal GH secretion and GH responses to GH-releasing hormone (GHRH) in untreated and estrogen-treated male rats (200 micrograms estradiol valerate s.c., 1 single dose 3 days before the experiment or every 3 days for 2 weeks). All the experiments were carried out in rats anesthetized with pentobarbital. GH responses to GHRH (1 microgram/kg) were inhibited by bombesin (100 micrograms/kg) in untreated rats, but were markedly increased in rats treated with estrogens either 3 days before or for the previous 2 weeks. Similarly, bombesin administration (25 or 100 micrograms/kg) in estrogen-treated rats induced a clear-cut, dose-related increase in basal GH levels. This stimulatory effect of bombesin was not affected by passive immunization with antisomatostatin antiserum (750 microliters i.v., 60 min before) and only partially blocked by anti-rGHRH antiserum (750 microliters i.v., 1 h before). In conclusion, our data show that bombesin exerts an inhibitory effect in normal male rats but a stimulatory one in estrogenized rats. This latter effect is independent of somatostatin and only partially blocked by anti-rGHRH serum.

Animals↗