Abstract
Abstract
To study the effects of time in culture on prolactin (PRL) and growth hormone (GH) responses to exogenous stimuli, bromocriptine (10−7 M) or somatostatin (10−7 M) were added to primary cultures of dispersed rat anterior pituitary cells (DC). Cells which had been in culture for 3, 6, or 9 days were then incubated for 6 hr and the media were radioimmunoassayed for PRL and GH. The inhibitory effects of bromocriptine on PRL release (76% decrease) and somatostatin on GH release (62% decrease) from cultured cells were maximal on Day 3 and decreased with age of the culture. In addition, the inhibitory effect of bromocriptine on GH release (32% decrease) was slight but maximal on Day 3 and decreased with time in culture. In contrast, somatostatin showed slight and stable inhibition of PRL release (26 to 29% decrease) at each of the three time periods. At the end of each incubation, the media were replaced with Ham's F-10 medium lacking bromocriptine or somatostatin and the cultures were incubated again for 6 hr. Even after removal of these agents, the inhibitory effects of bromocriptine on PRL or somatostatin on GH release persisted at almost the same or a higher degree compared to the controls. On the other hand, the inhibitory effects of bromocriptine on GH or somatostatin on PRL disappeared almost completely after removal of the agents. The release of both PRL and GH into the media was greater in all cases, including the controls, during the second incubation. This may have been due in part to the stimulation caused by changing the media. The results suggest: (1) rat pituitary mammotrophs and somatotrophs may both possess receptors for bromocriptine and somatostatin (2) in the absence of hypothalamic control (i.e., in vitro system), these cells are most sensitive to both agents on Day 3, and (3) the rebound increases seen in vivo following these agents are likely caused by hypothalamic modulations.
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