THE DURATION OF PROLACTIN SECRETORY BURSTS FROM THE PITUITARY IS INDEPENDENT FROM BOTH PROLACTIN AND GONADAL-STEROID PLASMA-LEVELS IN WOMENAND IN MEN

The intrinsic secretory characteristics of prolactin (PRL) have been i nvestigated using newly developed algorhythms for instantaneous secret ory rate (ISR) computation. PRL secretory rate, its intrinsic pulsatil e characteristics and their possible dependance from gonadal steroids were investigated in five groups of subjects: a) 11 women during the f ollicular and luteal phase of the same menstrual cycle; b) 5 healthy p ostmenopausal women; c) 6 women affected by functional hyperprolactine mia; d) 5 normal men; e) 4 agonadal subjects before and during testost erone replacement therapy. All subjects underwent a 6 hours pulsatilit y study, from 08:00 to 14:00, sampling every 10 minutes. PRL plasma co ncentrations were determined using a RIA system and the presence of PR L secretory pulses was evaluated with program DETECT, both on plasma t ime series and after ISR computation. A distinct PRL episodic release was observed in all groups (follicular phase: 5.5+/-0.5, luteal phase: 6.5+/-0.6, postmenopause: 5+/-1, hyperprolactinemic women: 4.2+/-0.8, men: 4.8+/-0.4, agonadal before testosterone: 6+/-1, agonadal during testosterone administration: 5.3+/-0.3 peaks/6h),but mainly the comput ation of ISR allowed to demonstrate that the duration of the lactotrop es secretory events was constant in all groups studied. PRL secretory bursts duration ranged between 23.1+/-1.8 and 25.4+/-2.5 minutes indep endently both on PRL or on sex steroid plasma levels. In conclusion, t he present report shows that in different physiological conditions the intrinsic secretory bursts from lactotropes are constant in duration independently from the functional state, sex and the steroid hormone l evels.