Effects of propranolol on GH responsiveness to repeated GH-releasing hormone stimulations in normal subjects

Abstract

Abstract. The influence of β-adrenergic blockade by oral propranolol on the variability of GH responses to GHRH and on GH responsiveness to repeated GHRH administrations was investigated. Eight normal volunteers underwent three tests on three separate occasions. Each test consisted of two administrations of 80 μg GHRH at 2-h intervals without other medication (test 1) or combined with oral administration of 80 mg propranolol 90 min before the first (test 2) or the second GHRH injection (test 3). In test 1 GH levels increased significantly after the first, but not the second GHRH bolus (net incremental area under the curve [nAUC], mean ± sd: 1453 ± 974 and 178 ± 309 μg·l−1·(120 min)−1, respectively). In test 2 basal GH secretion was not influenced by propranolol administration, whereas the GH response to the first GHRH injection was significantly greater than in test 1 (2327 ± 1814 μg·l−1·(120 min)−1; p<0.05). However, individual subjects showed the same variability of GH response as in test 1. The GH response to the second GHRH bolus remained negligible. In test 3 administration of propranolol 90 min before the second GHRH bolus led to a clear GH increase (690±1002 μg·l−1·(120 min)−1), not significantly different from the GH response to the first bolus (1796±1375 μg·l−1·(120 min)−1). However, only 4 subjects showed a marked restoration of the GH responsiveness to the second GHRH administration. In conclusion, oral administration of propranolol is able to increase GH responsiveness to GHRH without changing the great individual variability. The response to a repeated GHRH stimulation is only partially restored by propranolol.

The effect of repeated administration of hexarelin, a growth hormone releasing peptide, and growth hormone releasing hormone on growth hormone responsivity

“…The GH response to repeated boluses of GHRH-(1-29)-NH 2 in our study was preserved. This contrasts with the attenuated response to the second bolus of GHRH observed by others (Massara et al, 1986;Ghigo et al, 1989;Arosio et al, 1990;Arvat et al, 1992). Possible reasons for this include different dosing regimens (dosage used and time interval between successive boluses) and/or different types of GHRH used in the various studies.…”

Eifects of consecutive doses of GHRH on OH secretion

“…is maintained after two consecutive doses of GHRH (1-29) (50, 100 and 200 pg/bolus), although the second GH responses are always significantly less than the first. In our and other's hands (Sartorio et al, 1986(Sartorio et al, , 1988Losa et al, 1986;Ghigo et al, 1989;Arosio et al, 1990) repeated GHRH administration (either at a dose/bolus of 1 pg/kg or at a standard dose of 50 or 80 pg i.v.) at intervals of 2 hours leads to a significant reduction in GH responsiveness (evaluated as net incremental area under the GH curve (GHnAUC) over 60 and 120 minutes after each bolus) to the second GHRH administration in normal adults.…”

Divergence between growth hormone responses to insulin‐induced hypoglycaemia and growth hormone‐releasing hormone in patients with non‐functioning pituitary macroadenomas and hyperprolactinaemia

“…This phenomenon has been reemphasized in a recent study that failed to show a significant correlation between peak GH levels obtained with repeated ITTs in healthy subjects (Hoeck et al, 1995). Such a variable peak GH level is also observed after GHRH stimulation (Arosio et al, 1990). Given the highly pulsatile nature of pituitary GH secretion (Iranmanesh & Veldhuis, 1992), these findings are not surprising.…”