Possible interactions of cyclosporine and hyperprolactinemia modulating the episodic secretion of prolactin.

The interrelationship between the effects of prolactin and cyclosporine (CsA) appears to be very complex and until now poorly understood. The aim of the present work was to analyze whether chronic treatment with CsA could modify the episodic secretion of prolactin in male rats and whether the presence of an ectopic pituitary could counteract the effects of the drug on the pulsatile secretion pattern of this hormone. At 30 days of age, male rats were implanted with one anterior pituitary under the kidney capsule or where sham-operated. Both pituitary-grafted and sham-operated rats were injected sc for 30 days with the vehicle or CsA (5 mg/kg/day), beginning on the day of surgery. Pituitary grafting and/or CsA administration changed the pulsatile secretion pattern of prolactin. In pituitary-grafted male rats, mean serum prolactin levels, absolute pulse amplitude, and half-life of the hormone increased, while the pulse frequency decreased, compared with the values found in sham-operated rats. CsA administration to sham-operated rats increased the relative amplitude of prolactin peaks and diminished the half-life of the hormone, compared with rats of the same group treated with vehicle. However, CsA treatment in pituitary grafted rats led to lower mean serum prolactin levels and absolute amplitude, while the frequency, duration, and relative amplitude of prolactin pulses were not modified. Plasma prolactin levels did not change in control animals, whereas a reduction in circulating values of the hormone was found in pituitary grafted animals. These data suggest that CsA modifies the pulsatile secretory pattern of prolactin in pituitary-grafted male rats. The different effects observed in the control and pituitary-grafted animals might be due to a direct effect of the drug on the ectopic lactotrophs that are submitted to local regulatory influences different from those of the in situ pituitary which are submitted to the regulatory influence of the hypothalamus.