Failure of the gamma-aminobutyric acid (GABA) derivative, baclofen, to stimulate growth hormone secretion in heroin addicts.

In order to establish possible alterations in the gamma aminobutyric acid (GABA)ergic control of growth hormone (GH) secretion in heroin addicts, ten patients (age, 25.8 +/- 1.07 yr (mean +/- SE); duration of heroin addiction, range 3-8 yr; weight, 67.3 +/- 0.87 kg body weight), and ten age (29.1 +/- 0.84 yr)- and weight (69.7 +/- 0.87 kg)-matched normal controls were tested with the GABAergic B-receptor agonist baclofen (10 mg p.o. at 09.00 h) (experimental test) or a placebo (control test). Blood samples for GH assay were taken every 15 min for the next 150 min. Normal controls underwent one control and one experimental test. Heroin addicts were submitted to both baclofen and placebo test twice, once around the time of their admission to a recovery community for drug abusers, when they were still assuming heroin, and again after two months of permanence in the community. From the time of their admission to the community, the patients were forbidden to use heroin. For two weeks after admission they were treated with clonidine and acetylsalicilic acid to attenuate withdrawal symptoms. Thereafter, the patients underwent a period of wash-out of pharmacological treatments for at least 6 weeks before being retested. Basal GH levels were similar in normal controls and heroin addicts in all tests and remained unmodified during control tests in all subjects. The administration of baclofen increased four times the serum GH levels within 120 minutes in the normal controls, whereas it did not modify serum GH concentrations in heroin addicts either during the period of drug abuse or after two months of abstinence. These data show that the control of GH secretion mediated by GABAergic B-receptors is impaired in heroin addicts. It is hypothesized that this neuroendocrine alteration might represent a trait marker of heroin addiction, or more likely, that it was a consequence of a long addiction to heroin persisting after two months of abstinence.