Lack of episodic growth hormone secretion in rats with anterolateral deafferentation of the medial-basal hypothalamus.

Growth hormone secretory dynamics were studied in rats sampled through chronic indwelling right atrial cannulae at time-intervals ranging from 2 days to 2 months after placing an anterolateral cut (ALC) around the medial-basal hypothalamus (MBH). The episodic secretion normally occurring in the control animals could not be seen in the rats with an ALC. Instead of the usual high bursts and low trough levels occurring between 09.00 and 13.00 h in the controls, the operated animals had fairly constant plasma GH levels with only minor fluctuations at all postoperative time-points studied. These results suggest that (1) the isolated MBH is incapable of maintaining the episodic secretion of GH and (2) the pulsatile hormone release is dependent on neural pathways entering the MBH from an anterolateral direction.