Effects of phenylalanine, histidine, and leucine on basal and GHRH-stimulated GH secretion and on PRL, insulin, and glucose levels in short children, comparison with the effects of arginine

Of the amino acids arginine is the most potent GH secretagogue in man, It potentiates the GH response to GBRH, exerts a weaker PRL-releasing effect, stimulates insulin and glucagon and induces a biphasic glucose variation, The potency and effects of other amino acids on pituitary and pancreatic hormones need to be clarified, In 43 children with normal short stature (5.3-14.0 yr; 30 M and 13 F) the effects of the infusion of phenylalanine (Phe, 0.08 g/kg), histidine (His, 0.1 g/kg), and leucine (Leu, 0.08 g/kg) on basal and GHRH-stimulated GH secretion and on PRL, insulin and glucose levels were studied and compared with those of arginine at high (hArg, 0.5 g/kg) or low dose (lArg, 0.2 g/kg), Phe increased basal (p<0.05) but not GHRH-stimulated GH levels, induced PRL and insulin rises (p<0.03 and p<0.03), and did not change glycemia, Though a trend toward an increase in basal GH levels was found after His, His and Leu did not significantly modify either basal or GHRH-induced GH secretion nor basal PRL, insulin and glucose levels, Both hArg and lArg increased basal (p<0.0001 and p<0.05, respectively) and GHRH-stimulated GH levels (p<0.006 and p<0.006), hArg increased both PRL (p<0.002) and insulin levels (p<0.005) more (p<0.0005 and p<0.004) than lArg (p<0.005 and p<0.005), while glucose levels showed a similar increase followed by a similar decrease, We conclude that in childhood: a) Phe significantly increases GH secretion but, differently from Arg, does not potentiate the response to GBRH, suggesting different mechanisms of action of these amino acids; b) differently from His and Leu, Phe is a PRL and insulin secretagogue but is less potent than Arg; c) Arg has the highest stimulatory effect on pituitary and pancreatic hormones

Freshwater phytoplankton diversity: models, drivers and implications for ecosystem properties

Our understanding on phytoplankton diversity has largely been progressing since the publication of Hutchinson on the paradox of the plankton. In this paper, we summarise some major steps in phytoplankton ecology in the context of mechanisms underlying phytoplankton diversity. Here, we provide a framework for phytoplankton community assembly and an overview of measures on taxonomic and functional diversity. We show how ecological theories on species competition together with modelling approaches and laboratory experiments helped understand species coexistence and maintenance of diversity in phytoplankton. The non-equilibrium nature of phytoplankton and the role of disturbances in shaping diversity are also discussed. Furthermore, we discuss the role of water body size, productivity of habitats and temperature on phytoplankton species richness, and how diversity may affect the functioning of lake ecosystems. At last, we give an insight into molecular tools that have emerged in the last decades and argue how it has broadened our perspective on microbial diversity. Besides historical backgrounds, some critical comments have also been mad