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Biomedical subjects

F Mena

Publications and source records attributed to F Mena.

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

Ether releases large amounts of prolactin from rat pituitaries previously "depleted" by short term suckling.

The effect of ether inhalation upon plasma PRL levels was assessed in lactating rats whose pituitary stores of the hormone first had been depleted by a short term (10-min) period of suckling in comparison with those whose PRL stores had not been depleted by prior suckling. Ether, unlike suckling or handling-decapitation stress, did not deplete pituitary PRL and caused only a small increase (36 to 52 ng/ml) in the plasma concentration of the hormone. However, when ether was given 10, 60, or 120 min after the plasma concentration had subsided from a prior 10-min period of suckling, the plasma concentration of PRL in each instance rose within 5--10 min to 200--250 ng/ml and was sustained at that level for the remainder of the 30-min exposure period. The amplitude and profile of the plasma PRL concentration after ether inhalation were similar to those obtained when a second suckling, rather than ether, was administered after the short term suckling. These data support the hypothesis that releasable PRL derives from depleted PRL and also indicate that, once it is formed, releasable PRL remains available for discharge into the circulation for a relatively long period of time.

Animals↗
PubMed1977

Metabolic clearance of rat prolactin in the lactating and non-lactating rat.

The metabolic clearance of rat prolactin, assessed by the continuous infusion to equilibrium method, increased from 0-77 to 2-15 ml/min in lactating and from 0-65 to 1-75 ml/min in non-lactating rats as the infusion rate was increased from 100 to 472 ng/min. The clearance rate of rat prolactin did not increase when large doses of ovine prolactin were infused simultaneously with rat prolactin. The clearance rates computed from equilibrium levels of immunoreactive 131I-labelled rat prolactin in plasma were highly correlated with, but were considerably greater than, those computed from unlabelled rat prolactin which was infused simultaneously. In lactating and non-lactating rats, the clearance of each prolactin tested (RP-1, B-1, Nicoll's secreted and 131I-labelled) increased and had stabilized within the 30-35 min of infusion of each new higher dose of the hormone. The ability of the rat to clear quickly greater amounts of prolactin from the circulation as the infusion rate increases implies that plasma prolactin concentrations do not necessarily mirror the rate of prolactin secretion from the pituitary.

Animals↗
PubMed1976

Effect of suckling on plasma prolactin and hypothalamic monoamine levels in the rat.

In lactating rats that were separated from their pups for 8 hours, suckling induced a rapid rise in plasma prolactin levels. Correlatively, it induced a depletion in dopamine (DA) and serotonin (5-HT) Concentrations within the hypothalamus as early as 5 min after the onset of suckling. This depletion lasted as long as the stimulus was maintained. A parallel increase in the level of the metabolite of 5-HT, 5-hydroxyindolacetic acid (5-HIAA), was observed. Under these conditons, the ratio of 5-HIAA/5-HT is augmented. This ratio is a good index of turnover of the transmitter. Suckling affected neither the content of noradrenaline (NA) in the hypothalamus nor the levels of any amine tested in the cerebral cortex. When pups were separated from their mother for 24 hours, suckling no longer resulted in changes in either plasma prolactin levels or hypothalamic DA, 5-HT, or 5-HIAA concentrations. We have concluded that the activation of a discrete system of 5-HT containing neurons is associated with the triggering effect of suckling on prolactin release.

Animals↗
PubMed1976

Analysis of suckling-induced changes in adenohypophyseal prolactin concentration in the lactating rat by three assay methods.

Suckling-induced changes in adenohypophyseal prolactin (PRL) concentrations in lactating rats were measured in two experiments by three assays: a disc electrophoretic assay (DEA), a bioassay (BA) and a radioimmunoassay (RIA). Substantial discrepancies among the three assays were found in the absolute amounts of pituitary PRL measured and in the changes in adenohypophyseal PRL concentration that were recorded between suckling intervals. The results indicate that in dynamic states of secretory activity the correspondence among BA, RIA and DEA estimates of pituitary PRL concentration is poor.

Animals↗
PubMed1975

Milk secretory response of the conscious lactating rat following intravenous injections of rat prolactin.

Mammary glands of rats on day 14 of lactation were emptied of milk by the pups after 8 h of nonsuckling with the aid of oxytocin injections to the mother. The glands subsequently refilled about 50% within 6 h and were completely refilled with mild within 16 h. Suckling for 5 min midway during the 8 h period of nonsuckling caused complete refilling of the glands within 6 h. Refilling within 6 h also occurred if, instead of suckling, rat prolactin was injected at 1 min intervals directly into the circulation of the conscious mother via an indwelling right atrial catheter. Five injections of 200 ng or three injections of 400 ng were without effect (in comparison with five injections of saline) upon mammary refilling whereas 10 injections of 200 ng or four injections of 400 ng simulated significant but submaximal refilling. Complete refilling resulted from five injections of 400 ng. Prolactin is secreted steadily over prolonged periods of suckling in the rat, but only that prolactin released during the first few minutes of suckling appears to be required for milk secretion.

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