The effect of the somatostatin analog SMS 201-995 on normal growth hormone secretion in the rat. A comparison with the effect of bromocriptine on normal prolactin secretion

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Published on Monday, 31 December 2018

Abstract

The somatostatin analog SMS 201-995 was recently shown to be effective in suppressing GH secretion and in causing tumour shrinkage in patients with GH-secreting pituitary tumours.

In this respect, the action of SMS 201-995 seems similar to that of the dopamine-agonist bromocriptine in patients with PRL-secreting pituitary tumours.

In the present study we compared the respective effects of SMS 201-995 and bromocriptine on normal rat GH and PRL release in vivo and in vitro.

Both in vitro and in vivo, repeated administration of SMS for up till 6 days suppressed circulating GH concentrations, and the ability of the pituitary glands to release GH in vitro. A dose-dependent diminution occurred of the total pituitary GH content in rats treated in vivo with SMS 201-995 for 4-6 days.

During short-term in vitro incubation for only 4 h, the total amount of GH measured in the medium + gland was also diminished. Chronic administration with SMS 201-995 (2 micrograms/kg twice daily for 15 days), however, resulted in a complete desensitization of its inhibitory effect on GH synthesis and release.

In similar experiments it was shown that the dopamine agonist bromocriptine affects normal PRL secretion in a different manner.

Both in vitro (10 nmol/l) and in vivo administration for 6 days (0.2 mg/kg twice daily) greatly inhibited circulating PRL levels and the ability of the pituitary glands to release PRL in vitro.

This is, however, in all instances accompanied by an accumulation of PRL within the pituitary gland.

Long-term bromocriptine administration (0.2 mg/kg twice daily for 15 days) inhibited PRL secretion, and finally also a decrease in the total pituitary PRL content was observed.

It is shown in this study that SMS 201-995 and bromocriptine affect hormone release by normal pituitary glands in a different manner. SMS 201-995 acutely inhibits GH release and diminishes within a few hours of exposure also the GH content in normal cells by a powerful inhibition of GH synthesis and/or an increase in intracellular degradation of GH.

Bromocriptine, however, exerts primarily an inhibitory effect on PRL release, whereas an inhibition of synthesis and/or degradation of intracellular PRL is evident only after long-term exposure to the drug.

 



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See also:

- Official Web Site: The Di Bella Method;

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