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Blindness Impairs Plasma Growth Hormone Response to L-Dopa but not to Arginine^*

Institute of Endocrinology, First Faculty of Medicine, University of Naples Naples, Italy

Address all correspondence and requests for reprints to: A. Bella-stella, S. Antonio a Posillipo 85, 80122 Naples, Italy.

To investigate how blindness influences GH secretion, we studied the GH response to L-dopa and arginine in 8 blind adult males and 10 normal age-matched control males. Arginine and L-dopa tests were performed in random order at least 1 week apart at 0800 h, and plasma GH was measured by RIA.

The blind subjects showed GH responses to arginine similar to those in normal subjects [peak, 22.1 ± 1.3 vs. 20.5 ± 1.3 µg/L (±SE)], but their GH response to L-dopa was significantly reduced [peak, 5.4 ± 1.3 vs. 20.3 ± 2.4 µg/L (±SE); P < 0.01]. Because L-dopa is believed to release GH by stimulating endog-enous GHRH, whereas arginine may act by suppressing endog-enous somatostatin secretion, we propose that blindness may impair GH release by inhibiting GHRH secretion.

^* This work was supported in part by a grant from MPI, Rome, Italy (60%), 1987.

Received August 7, 1989.