Episodic growth hormone secretory patterns in sheep: relationship to gonadal steroid hormones.

Abstract

The influence of anabolic steroids on growth hormone (GH) secretion in ruminants remains unclear, perhaps because of the dynamic nature of GH secretion. In the present study, blood samples were obtained at 15-min intervals for 12 h from intact ram lambs, ram lambs castrated postpubertally, and castrated ram lambs treated with either testosterone propionate (TP) or diethylstilbestrol (DES). Intact rams exhibited GH secretory episodes of greater (P less than 0.01) amplitude than did castrated lambs. Similarly, mean base-line and mean overall GH concentrations were higher (P less than 0.01) in rams than in castrates. Treatment of castrates with either TP or DES resulted in increased base-line (P less than 0.05) and overall (P less than 0.05) GH concentrations compared to untreated castrates. Although amplitude of GH spikes was larger in TP and DES groups, this difference was not statistically significant (P greater than 0.05). Because numerous studies have demonstrated that intact rams and castrates treated with TP or DES grow faster than untreated castrates, the data in the present study support the hypothesis that the anabolic action of androgens and estrogens is due, at least in part, to their influence on GH secretion.

Episodic growth hormone secretion in sheep in relation to time of feeding, spontaneous meals and short term fasting.

“…These data confirm the findings of other workers (Chamley et al 1974;Bassett, 1974a;Davis et al 1977) that sheep in common with other ruminants (cattle, Blom et al 1976;goats, Tindal, Knaggs, Hart & Blake, 1978) secrete GH in an episodic fashion with several peaks over 24 hr.…”

Androgen-mediated down-regulation of CYP1A subfamily genes in the pig liver

“…This hypothesis is further supported by the present findings that in spite of sex difference in the secretion profile of GH in Landrace pigs (Arbona et al 1988), there was no sex difference in the constitutive expression of hepatic CYP1A subfamily enzymes. On the other hand, the modification of the secretion profile of GH by androgen administration had been reported (Davis et al 1977, Somana et al 1978, Link et al 1986, Dubreuil et al 1989. Accordingly, drastic decreases in the levels of CYP1A subfamily enzymes in androgen-treated Landrace pigs might occur, at least in part, through the change in secretion profile of GH, especially the emphasis of a male-type secretion profile.…”

Characteristics of growth hormone response to the administration of growth hormone-releasing hormone (GRF) in the lamb

“…Because in this experiment the interval between the different peaks is only a few minutes, it is obvious that we are describing a different phenomenon. In the lamb, endogenous GH peaks have been described previously as monophasic (Davis et al, 1977). However, our use of more frequent blood sampling periods has allowed us to observe multiphasic episodic secretory peaks.…”