Inhibition by phospholipid liposomes of the prolactin and cortisol response to insulin hypoglycemia in man
This study was designed to further investigate the purported dopaminergic activity of phospholipid liposomes (PL) prepared from bovine cerebral extracts, and to obtain further indications about their pituitary or suprapituitary site of action. In eight normal subjects, we have studied the effects of PL administration (250 mg as IV bolus plus additional 250 mg infused IV over a 60-min period), compared to placebo, on the prolactin (PRL), cortisol and growth hormone (GH) response to an insulin tolerance test (ITT). In eight additional subjects, the effects of PL on the PRL and TSH response to TRH were evaluated. PL medication blunted the PRL and cortisol response in the ITT: significant differences, with respect to placebo administration, were observed between mean peak PRL values (51.9±13.63 SEM vs 83.4±26.35 ng/ml, P<0.05) and mean cortisol values at 120 min time (20.9±0.67 vs 26.7±2.46 μg/dl, P<0.05). In contrast, PL administration did not modify the ITT-related GH rise or the PRL and TSH release in response to TRH. These findings favour the view that PL are endowed with intrinsic biological activity which is dopamine-mediated, and point to the hypothalamus as their primary site of action.