This study examined effects of intracerebroventricularly (i.c.v.) administered somatostatin (SRIH-14 and SRIH-28) on growth and function of pituitary somatotropes (GH cells) and lactotropes (PRL cells). Male rats received three i.c.v. injections (1 µg/5 µl) of SRIH-14 or SRIH-28 every second day. Blood samples were collected for hormone assays and pituitaries were removed for histological and morphometric evaluation 5 days after the last i.c.v. treatment. Compared to control animals, SRIH treatment decreased (p < 0.05) pituitary weight and all morphometric measurements obtained in GH and PRL cells. Concentrations of serum growth hormone (GH) and prolactin (PRL) in both SRIH-treated groups were also lower (p < 0.05) than in control rats. These findings suggest that centrally administered somatostatin is specifically involved in the control of growth and secretory activity of GH and PRL cells. Thus, pharmacological manipulation of SRIH receptors reached from cerebrospinal fluid may alter systemic effects of GH and PRL.

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The structure and function of C cells of middle-aged female rats (14-months old) treated with estradiol dipropionate (EDP), calcium (Ca) or a combination of EDP+Ca were studied. A stereological method was used to determine the volume of calcitonin (CT)-immunoreactive C cells and their nuclei, and the relative volume density and mean number of the C cells per section were calculated. Serum levels of CT, osteocalcin, parathyroid hormone (PTH), and beta-estradiol were also measured. A significant decrease in body weight of the rats treated with EDP or EDP+Ca was observed. These treatments led to a significant decrease in cellular and nuclear volumes, relative volume density, and mean number of C cells per section, in comparison with the corresponding controls. A reduction of the serum level of CT, PTH, and osteocalcin was also recorded in EDP- and EDP+Ca-treated animals. No statistically significant differences between Ca- and vehicle-injected rats, with regard to all morphometric C cell parameters and biochemical values determined, were seen. However, a conspicuous degranulation of the C cells and decreased immunoreactivity for CT in the Ca-receiving group, which could be interpreted as the signs of increased activity of these cells, were noticed. This effect of Ca was also observed in rats injected with EDP and Ca in combination, when the inhibitory effect of EDP on C cell function was less noticeable than in the group treated with EDP alone.

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