Retinoic acid inhibits in vivo thyroid-stimulating hormone secretion

Retinoids are needed for normal growth and development. Retinoic acid (RA), an active metabolite of vitamin A, acts through nuclear receptors that belongs to the superfamily which also includes the T3 receptors and 1-25-dihydroxyvitamin D receptor. In order to assess whether RA is a regulator of in vivo thyroid-stimulating hormone (TSH) secretion, we studied the effect of RA administration on spontaneous basal TSH secretion and TSH responses to TRH in either euthyroid or hypothyroid rats. We found that rats treated with RA showed a decrease in spontaneous basal TSH levels and TSH responses to TRH. Similarly, RA administration to hypothyroid rats led to a decrease on TSH responses to TRH. Our data suggests that RA plays an important inhibitory role on in vivo secretion and this effect is unrelated to the thyroid status of the animals.

Acute ethanol administration in diestrus-2 in the rat on pulsatile prolactin and LH release

Exposure to ethanol is followed by changes in reproductive function in man and animals, characterized by modifications in the secretion patterns of prolactin and luteinizing hormone (LH). As both hormones are secreted in an episodic fashion, the present work was undertaken to study the effects of acute ethanol administration on pulsatile prolactin and LH secretion patterns in adult female rats. Rats were previously cannulated to allow a continuous blood withdrawal to study the pulsatile patterns of prolactin and LH. The mean values of prolactin during the bleeding period and the absolute pulse amplitude of prolactin peaks were significantly increased by acute ethanol administration, whereas a significant decrease of relative pulse amplitude and frequency of this hormone was observed. On the other hand, ethanol administration increased the mean serum LH levels and the absolute and relative amplitudes of LH peaks. Ethanol treatment did not modify either frequency or duration of LH peaks. These data suggest that acute ethanol administration in adult female rats is followed by changes in the pulsatile prolactin and LH secretory patterns, which might be part of the mechanism to explain ethanol effects on the endocrine system.

Steroids in severe head injury: A prospective randomized clinical trial

This is a prospective randomized study of the efficacy of steroid therapy in patients with severe head injury. One hundred patients were randomized into two equal groups: the steroid group received 5 mg/kg/day of methylprednisolone, and the nonsteroid group received no drug. The groups were similar in their clinical features. All patients received a standardized therapeutic regimen. The patients were also classified as early responders or nonresponders to the overall treatment protocol without regard to steroid administration, on the basis of change in Glasgow Coma Scale score during the first 3 days of admission. There was no statistically significant difference in the outcome of the steroid and nonsteroid group at 6 months. Of the responders who were on steroids, 74% had good outcomes or were disabled, compared with 56% of the responders who did not receive steroids. In the nonresponder group, the patients on steroids were actually associated with a worse outcome than those who did not receive steroids: 75% of the nonresponders who received steroids were dead or vegetative, compared to 56% of those who were not receiving steroids. The data suggest that: 1) the effect of steroids may be different for different patient groups; 2) in order to identify these patients, a sensitive coma scale is needed; and 3) a rational approach to steroid therapy in head-injured patients may be to start all patients on steroids, but to discontinue their use in patients identified as not benefiting from steroid therapy.