Rapid changes in growth hormone regulation and hypothalamic somatostatin after transection of anterolateral pathways to the medial-basal hypothalamus in the rat.

Plasma and pituitary GH content, in-vitro GH release and somatostatin-like immunoreactivity (SLI) in the stalk-median eminence were studied up to 7 days after making an anterolateral cut (ALC) around the medial-basal hypothalamus. Plasma GH concentration increased within 15 min to a very high level, then fell to a high level which was unchanged for several hours. The GH concentration then steadily decreased between days 2 and 7. The SLI content in the stalk-median eminence decreased to 3.5% of the control value within 3 days. The GH content of the anterior pituitary gland was 58.8% of the control value by 1 week after the operation but the in-vitro sensitivity to somatostatin of the GH cells failed to change. Pentobarbitone injection stimulated GH release in the sham-operated controls but decreased it in the rats with an ALC. These findings suggest that transection of somatostatin-containing fibres is followed by a rapid rise and a lasting high concentration of plasma GH which slowly returns towards lower levels in parallel with a marked depletion of pituitary GH content. In rats with transected somatostatin innervation of the median eminence, sodium pentobarbitone probably decreases GH secretion by depressing the secretion of GH-releasing hormone.