Title : Effects of single and short-term administration of clonidine on hypothalamic-pituitary somatotropic function of the adult male rat: an in situ hybridization study.

Pub. Date : 1996 Feb

PMID : 8632352






6 Functional Relationships(s)
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1 Acute administration of CLO significantly decreased hypothalamic GHRH content [leaving unaltered GHRH messenger RNA (mRNA) levels] and increased plasma GH levels; hypothalamic SS content/mRNA levels and pituitary GH content/mRNA levels remained unchanged. Clonidine growth hormone releasing hormone Rattus norvegicus
2 In 1- and 3-day CLO-treated rats, by contrast, decreased hypothalamic GHRH content was coupled with a significant reduction in GHRH mRNA levels. Clonidine growth hormone releasing hormone Rattus norvegicus
3 In 6-day CLO-treated rats, hypothalamic GHRH content and mRNA levels were still significantly reduced, plasma GH levels were increased, but to a lesser extent than in 1- and 3-day CLO-treated rats, and pituitary GH content and mRNA reverted to control levels. Clonidine growth hormone releasing hormone Rattus norvegicus
4 These results indicate that 1) functional activation of alpha-2 adrenergic receptors by CLO increases GHRH release from the hypothalamus, 2) CLO, via GHRH, increases GH secretion and biosynthesis, which in turn feeds back in the hypothalamus to reduce GHRH biosynthesis, and 3) reduction of hypothalamic GH-stimulatory activity tones down the initial pituitary somatotropic hyperfunction. Clonidine growth hormone releasing hormone Rattus norvegicus
5 These results indicate that 1) functional activation of alpha-2 adrenergic receptors by CLO increases GHRH release from the hypothalamus, 2) CLO, via GHRH, increases GH secretion and biosynthesis, which in turn feeds back in the hypothalamus to reduce GHRH biosynthesis, and 3) reduction of hypothalamic GH-stimulatory activity tones down the initial pituitary somatotropic hyperfunction. Clonidine growth hormone releasing hormone Rattus norvegicus
6 These results indicate that 1) functional activation of alpha-2 adrenergic receptors by CLO increases GHRH release from the hypothalamus, 2) CLO, via GHRH, increases GH secretion and biosynthesis, which in turn feeds back in the hypothalamus to reduce GHRH biosynthesis, and 3) reduction of hypothalamic GH-stimulatory activity tones down the initial pituitary somatotropic hyperfunction. Clonidine growth hormone releasing hormone Rattus norvegicus