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The present experiment was carried out to investigate the effects of exogenous adenosine 5'-triphosphate (ATP) and growth hormone (GH) on cellular H(+) efflux rate (extracellular acidification rate) and Ca(2+) concentration ([Ca(2+)](c)) in cloned bovine mammary epithelial cells (bMEC) raised from the mammary gland of a 26-day-pregnant Holstein heifer. Perifusion of 2-day cultured cells with a medium containing ATP (10, 100 and 1000 micromol/l) for 30 min caused a significant and concentration-dependent increase in the cellular H(+) efflux rate. ATP application (100 micromol/l) caused a transient and large increase in [Ca(2+)](c) in all cells. In contrast, perifusion with a medium containing bovine GH at 10, 50 and 250 ng/ml for 30 min caused a significant decrease in the cellular H(+) efflux rate in a concentration-dependent manner. However, bovine GH application (50 ng/ml) caused a small decrease followed by an increase, in some cases, in [Ca(2+)](c). In bMEC treated with lactogenic hormones (1 microgram/l prolactin, 1 nmol/ml dexamethasone and 5 microgram/ml insulin) for 2 days, the increased H(+) efflux rate induced by ATP was significantly reduced, whereas the negative response induced by GH was inversely and significantly changed to the positive. Treatment of the cells with lactogenic hormones reduced the increase in [Ca(2+)](c) induced by ATP stimulation, while it enhanced the increase in [Ca(2+)](c) induced by GH stimulation. Application of ATP or GH did not cause any significant changes in [pH](c). Treatment with lactogenic hormones enhanced GH receptor (GHR) transcription that was determined by RT-PCR. From these results, we conclude that exogenous application of ATP and GH causes prompt and significant responses in H(+) transport and [Ca(2+)](c) that were significantly changed in the opposite direction by the treatment with lactogenic hormones. The lactogenic hormone treatment also enhanced GHR transcription, which may change post-receptor signal transduction systems for both agents in the bMEC.

The effects of short-chain fatty acids (SCFA: acetate, propionate, and butyrate) on growth hormone (GH)-releasing hormone (GHRH)-induced GH secretion from pituitary somatotrophs were assessed on isolated anterior pituitary cells of goats. Cells were cultured in Dulbecco's modified Eagle's medium for 3 days, either in the presence (1, 3, or 10 mM) or in the absence of each SCFA, and then stimulated with GHRH (10−12to 10−7M) for 30 min, again in the presence of and at the concentration of SCFA used over the previous 3 days. In the cells cultured in the absence of SCFA, the addition of SCFA to the medium during the GHRH stimulation period did not significantly change GHRH-induced GH release. However, in cells cultured in the presence of either propionate (3 or 10 mM) or butyrate (1, 3, or 10 mM), the addition of SCFA to the medium during GHRH stimulation significantly reduced the GHRH-induced GH release. The inhibitory effects of SCFA were dependent on the concentrations of SCFA and were greater for butyrate than for propionate. In the cells cultured in the presence of butyrate, but not in the absence, the total GH production (the sum of the released GH and the remaining GH after stimulation) was also significantly reduced. The GHmRNA expression was reduced in the cells cultured with 10 mM butyrate, whereas it was enhanced by the stimulation with 10−7M GHRH. These findings suggest that propionate and butyrate may inhibit GHRH-induced GH release and GH production by caprine anterior pituitary cells.

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