Evidence for direct action of calcitonin in the rat pituitary gland

Abstract

Classic concepts of calcitonin (CT) function have focused on the effects of CT on calcium homeostasis. More recently CT actions on brain and pituitary have been investigated. In order to evaluate the effects of CT on the anterior pituitary gland we studied the action(s) of CT in vitro and visualized endogenous CT in adult male rat pituitary gland by immunocytochemistry on ultrathin sections obtained by cryoultramicomy. In vitro study using dispersed anterior pituitary cells indicated that CT stimulated the secretion of PRL, whereas the secretion of GH, TSH and LH was not affected. CT\ x=req-\ like immunoreactivity was observed in lactotropes only. The other pituitary cell types were not immunoreactive.In lactotropes, immunostaining was observed in the cytoplasm and in the nucleus. In the cytoplasm, CT-like immunoreactivity was visuzalized in the cytoplasmic matrix and in the secretory granules. In the nucleus, immunostaining was distributed primarly in the euchromatin, in the vincinity of heterochromatin region. CT-like immunoreactivity was also observed at the plasma membrane but was only scarce. No reaction product was found when anti-CT serum pre-incubated with CT was used. In conclusion, these results bring evidence for a direct action of CT on lactotrope regulation in vitro as well as in intact animals. Calcitonin (CT), a 32 amino acid peptide with a 1,7-disulfide bridge and a proline amide at the carboxyl terminus, is synthesized by the C cells of the mammalian thyroid (Bussolati & Pearse 1967; Copp et al. 1962). Classic concepts of CT function have focused on the effects of CT on calcium homeostatis (Munson 1976). However, recent studies have indicated a broader range of CT action (Cantalamessa et al. 1978; Leicht et al. 1974) namely on the central nervous system (Freed et al. 1979; Morley et al. 1981). In addition, it has also been shown that CT can exert stimulatory or inhibitory action on the secretion of many adenohypophyseal hor¬ mones in basal conditions or in response to appro¬ priate stimuli (Cantalamessa et al. 1978; Pecile et al. 1981). Moreover, the presence of specific and saturable binding sites for CT have been recently demonstrated in the rat pituitary glands (Goltzman & Mitchell 1985; Maurer et al. 1983; Rizzo & Goltzman 1981). These different observa¬ tions suggest a possible involvement of CT in pitui¬ tary secretory activity. The aims of the present study were to investigate the in vitro effect(s) of CT on the release of adeno¬ hypophyseal hormone(s) and to demonstrate en¬ dogenous CT in anterior pituitary cell(s) at the subcellular level. Materials and Methods In vitro study Cell culture. Cell dispersion was performed according to Hospins 8c Farquhar (1973). Anterior pituitaries from Wistar female rats (Charle Rivers, France) were dissectedinto small pieces (about 0.5 mm in diameter) and incu¬ bated for 15 min with 0.5% trypsin in Dulbecco Minimum Essential Medium (DMEM) at 37°C. DNase (2 mg/1) was then added for 1 min to the medium. After enzymatic di¬ gestion the medium was removed an...

Hypothalamic Prolactin Receptor Messenger Ribonucleic Acid Levels, Prolactin Signaling, and Hyperprolactinemic Inhibition of Pulsatile Luteinizing Hormone Secretion Are Dependent on Estradiol

“…Calcitonin-like immunoreactivity is present in the CNS and in lactotrophs of the anterior lobe of the pituitary gland (1225). Calcitonin is most abundant in the inner portion of the anterior lobe (1595).…”