Ghigo E, Goffi S, Nicolosi M, Arvat E, Valente F, Mazza E, Ghigo M C, Camanni F
Department of Clinical Physiopathology, University of Turin, Italy.
J Clin Endocrinol Metab. 1990 Dec;71(6):1481-5. doi: 10.1210/jcem-71-6-1481.
At present, the mechanism(s) underlying the reduced spontaneous and stimulated GH secretion in aging is still unclear. To obtain new information on this mechanism(s), the GH responses to both single and combined administration of GH-releasing hormone (GHRH; 1 microgram/kg iv) and arginine (ARG; 30 g infused over 30 min), a well known GH secretagogue probably acting via inhibition of hypothalamic somatostatin release, were studied in seven elderly normal subjects and seven young healthy subjects. Basal GH levels were similar in both groups, while insulin-like growth factor-I levels were lower in elderly subjects (76.7 +/- 9.2 vs. 258.3 +/- 29.2 micrograms/L; P = 0.01). In aged subjects GHRH induced a GH increase (area under the curve, 314.9 +/- 91.9 micrograms/L.h) which was lower (P = 0.01) than that in young subjects (709.1 +/- 114.4 micrograms/L.h). On the other hand, the ARG-induced GH increase in the elderly was not significantly different from that in young subjects (372.8 +/- 81.8 vs. 470.6 +/- 126.5 micrograms/L.h). ARG potentiated GH responsiveness to GHRH in both elderly (1787.1 +/- 226.0 micrograms/L.h; P = 0.0001 vs. GHRH alone) and young subjects (2113.0 +/- 444.3 micrograms/L.h; P = 0.001 vs. GHRH alone). The potentiating effect of ARG on the GHRH-induced GH response was greater in elderly than in young subjects (1013.0 +/- 553.5% vs. 237.9 +/- 79.1%; P = 0.0001); thus, the GH increase induced by combined administration of ARG and GHRH overlapped in two groups. In conclusion, these results show that, differently from the GHRH-induced GH increase, the somatotroph response to combined administration of ARG and GHRH does not vary with age. Our finding suggests that an increased somatostatinergic activity may underlie the reduced GH secretion in normal aging.
目前，衰老过程中生长激素（GH）自发性分泌和刺激性分泌减少的潜在机制仍不清楚。为了获取有关该机制的新信息，我们在7名老年正常受试者和7名年轻健康受试者中研究了GH对生长激素释放激素（GHRH；1微克/千克静脉注射）和精氨酸（ARG；30克在30分钟内输注）单次及联合给药的反应，精氨酸是一种可能通过抑制下丘脑生长抑素释放起作用的著名GH促分泌剂。两组的基础GH水平相似，而老年受试者的胰岛素样生长因子-I水平较低（76.7±9.2对258.3±29.2微克/升；P = 0.01）。在老年受试者中，GHRH诱导GH升高（曲线下面积，314.9±91.9微克/升·小时），低于年轻受试者（709.1±114.4微克/升·小时；P = 0.01）。另一方面，老年受试者中ARG诱导的GH升高与年轻受试者无显著差异（372.8±81.8对470.6±126.5微克/升·小时）。ARG增强了老年（1787.1±226.0微克/升·小时；与单独使用GHRH相比，P = 0.0001）和年轻受试者（2113.0±444.3微克/升·小时；与单独使用GHRH相比，P = 0.001）对GHRH的GH反应性。ARG对GHRH诱导的GH反应的增强作用在老年受试者中比年轻受试者更大（1013.0±553.5%对237.9±79.1%；P = 0.0001）；因此，ARG和GHRH联合给药诱导的GH升高在两组中重叠。总之，这些结果表明，与GHRH诱导的GH升高不同，精氨酸和GHRH联合给药时生长激素细胞的反应不随年龄变化。我们的发现表明，生长抑素能活性增加可能是正常衰老过程中GH分泌减少的基础。
