Cholinergic action of thiopental on the hypothalamohypophyseal axis.

Ten postmenopausal women were divided into two groups. In five patients (group 1) four venous blood samples were collected at 5-minute intervals before and after thiopental sodium, 6 mg/kg IV, for determination of serum levels of prolactin and thyroid-stimulating hormone. In the other five patients (group 2) the procedure followed was as in group 1, but thiopental administration was preceded by atropine, 0.1 mg/10 kg. Prolactin levels increased significantly after thiopental injection in group 1, but not in group 2. Thyroid-stimulating hormone levels in both groups remained virtually unaltered. The fact that atropine prevented the increase of prolactin due to thiopental suggests that thiopental may have an indirect effect on the hypothalamohypophyseal axis through a cholinergic mechanism.