Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.1 (S1 nuclease)
 3,660 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Growth hormone (GH) suppresses its own secretion by stimulating somatostatin (SRIF) release. Thus, the possible regulation of GH-releasing factor (GRF) and SRIF release and SRIF messenger ribonucleic acid (mRNA) by GH was studied in the hypothalamus of male rats in vitro. The median eminences (ME's) were incubated in buffer containing 10(-7)-10(-11) M GH for 30 min. SRIF and GRF released into the medium were quantitated by RIA. The release of SRIF from ME fragments was significantly increased (P < 0.001) by 10(-9) M GH; however, 10(-9) M GH also inhibited (P < 0.01) GRF release from the ME. To determine the effect of GH on SRIF mRNA levels, periventricular nucleus (PeN) explants were cultured during 6 h in medium with 10(-7)-10(-11) M GH. Levels of SRIF mRNA (determined by an S1 nuclease protection assay) were significantly elevated in the presence of 10(-10)-10(-7) M GH. Likewise, 10(-9) M GH significantly stimulated SRIF release from PeN explants at 30 min and at 6 h. Surprisingly, 10(-9) M GH also significantly increased GRF release from the PeN explants at these times as well. This GRF was not responsible for the increased SRIF release or SRIF mRNA induced by GH since GRF antibody did not modify the GH-induced increases in SRIF release and mRNA levels. These results demonstrate a negative short-loop feedback of GH mediated at the ME by suppression of GRF and stimulation of SRIF release, whereas in the PeN GH increased both SRIF release and SRIF mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Growth hormone increases somatostatin release and messenger ribonucleic acid levels in the rat hypothalamus. 810 20

Growth hormone (GH) secretion from the pituitary is known to be under the dual control of GH-releasing factor (GRF) and somatostatin (SRIF). Hypothalamic SRIF, the major inhibitor of pituitary growth hormone secretion, inhibits its own release by a negative ultrashort-loop feedback mechanism. However, it is not known whether this negative regulation is mediated by inhibition of SRIF mRNA production. GRF may also inhibit its own release, thereby modifying pituitary GH secretion, possibly through an ultrashort-loop feedback mechanism. Thus, SRIF production and GRF release are both regulated by SRIF. Periventricular nucleus (PeN) and mediobasal hypothalamus (MBH) from adult male rats were incubated for 6 h in Waymouth's medium with either SRIF or the SRIF agonist analog RC 160 (10(-9) to 10(-6) M). Levels of SRIF mRNA were determined by an S1 nuclease protection assay using a 32[P]-labeled rat SRIF riboprobe. SRIF (10(-7) M) and RC 160 (10(-8), 10(-7) M) significantly (p< or =0.01) decreased SRIF mRNA levels in the PeN. The levels of SRIF mRNA in the MBH were not modified by either SRIF or RC 160. SRIF (10(-7) and 10(-6) M) significantly (p < or = 0.01 and p < or = 0.001, respectively) inhibited the release of GRF at 30 min in the MBH. Likewise, the release of GRF was slightly decreased by 10(-7) M RC 160, and significantly inhibited by 10(-6) M (p < or = 0.001) at 30 min. At 6 h, the levels of GRF were significantly reduced by 10(-7) M SRIF (p < or = 0.05) and by RC 160 (10(-7), 10(-6) M; p < or = 0.001 and p < or = 0.05, respectively). In contrast with these results, the SRIF analog was unable to alter SRIF release at 30 min. At 6 h incubation, RC 160 (10(-7) M) significantly (p < or = 0.001) reduced SRIF release from MBH fragments. These results demonstrate that SRIF and a SRIF analog decrease SRIF mRNA levels in the PeN and inhibit the release of SRIF from the nerve terminals of the MBH. Thus, SRIF appears to regulate its own gene expression by negative ultrashort-loop feedback. Therefore, when SRIF is secreted from these neurons in response to GRF, it down-regulates the preceding stimulatory input as well as its own secretion.
 ...
PMID:Somatostatin decreases somatostatin messenger ribonucleic acid levels in the rat periventricular nucleus. 986 65