Effect of prostaglandin A1 and A2 on thyrotropin secretion in rats

The effects of prostaglandin A1 and A2 (PG A1, A2) on secretion of thyrotropin (TSH) in vivo and in vitro were studied. Hundred micrograms per kg of PG A1 and A2 were injected i. v., and the animals were serially decapitated. Thyrotropin-releasing hormone (TRH), TSH and thyroid hormone were determined by radioimmunoassay. Effects of Pg A1 and A2 from anterior pituitary gland were also investigated by means of an in vitro experiment. Plasma and hypothalamic concentrations of immunoreactive TRH (ir-TRH) did not change after PG A1 and A2 injection. Basal plasma TSH levels significantly increased with a peak at 20 min after PG A1 and A2 injection. The plasma ir-TRH response to cold did not differ from that of the control, while the plasma TSH response to cold was significantly enhanced by PG A1 and A2. The plasma TSH response to TRH was also enhanced by PG A1 and A2. The plasma thyroid hormone did not change significantly after PG A1 and A2 injection. TSH release from anterior pituitary in vitro significantly increased after the addition of PG A1 and A2 to medium. These findings suggest that PG A1 and A2 stimulate TSH secretion from anterior pituitary in vivo and in vitro.