Objective: Ghrelin is a potent peptide stimulating GH secretion. Besides its direct action on the pituitary, ghrelin has been reported to stimulate GH release via the vagal afferent nerve in rats. To examine the involvement of vagal nerve in ghrelin-induced GH secretion in humans, GH responses to ghrelin were compared between vagotomized patients with gastrectomy and normal subjects.
Methods: Ghrelin (0.2 microg/kg) or GHRH (1 microg/kg) was administered intravenously in vagotomized patients and normal subjects on separate days, and plasma GH responses to the stimuli were examined.
Results: Ghrelin caused a significant plasma GH rise in both vagotomized patients and normal subjects. Peak GH levels in vagotomized patients (37.5+/-16.9 ng/ml) were not different from those in normal subjects (29.9+/-23.1 ng/ml). The areas under the curve of GH response to ghrelin did not differ between the two groups. GHRH also increased GH levels, and peak GH levels and areas under the curve after GHRH stimulation were also comparable between vagotomized patients and normal subjects.
Conclusions: In the present study, the involvement of the afferent vagal nerve in ghrelin-induced GH secretion was not confirmed in humans.