Dietary protein restriction stress and adrenocortical function: evidence for transient and long-term induction of enhanced cellular function.

Previous work has demonstrated that 4-week protein restriction of the domestic fowl (Gallus gallus domesticus) increases both adrenocortical cell sensitivity to ACTH and corticosteroidogenic capacity. In the present study we examined the transience (study 1) and the persistence (study 2) of this effect of protein restriction. In study 1, two strains of domestic fowl were used: a slower-growing White Leghorn strain and a faster-growing Cobb broiler strain. Cockerels (2 weeks old) were fed isocaloric diets containing either low (L; 5% or 8%) or control (C; 20%) levels of soy protein for 2 weeks, and then were either switched to the alternate diet (C-L, L-C) or maintained on the initial diet (C-C, L-L) for an additional 2 weeks. Cockerels were killed at 6 weeks of age. In study 2, White Leghorn cockerels (2 weeks old) were fed either diet for 4 weeks and then switched to or maintained on the control diet for an additional 4 weeks (i.e. C vs. restriction followed by repletion). In this study cockerels were killed at 10 weeks of age. In both studies highly enriched populations of adrenocortical cells were isolated from cockerel adrenal glands, and their steroidogenic properties (basal and maximally induced corticosterone and cAMP production; steroidogenic agent ED50 values) were evaluated in 2-h suspension incubations. In study 1, regardless of strain, the greater the length of the restriction period, the greater the magnitude of maximal cellular corticosterone production induced by ACTH; the average value for 4-week restriction (L-L) was 39.5% greater than that for 2-week restriction (L-C, C-L) and 117.5% greater than that for control (C-C). In addition, the value for restriction from 4-6 weeks of age (C-L) was 34% greater than that for restriction from 2-4 weeks of age (L-C), suggesting that the enhancement of maximal ACTH-induced corticosterone production after a 2-week restriction interval might be transient. Although there were no strain differences in the effect of protein restriction on maximal ACTH-induced corticosterone production, there were strain differences in its effect on cellular sensitivity to ACTH, as indicated by the ACTH ED50 values (the lower the ED50 value, the greater tha cellular sensitivity). With the White Leghorn strain, the greater the duration of protein restriction, the greater the adrenocortical cell sensitivity to ACTH; the sensitivity of L-L cells was 3.0 times the sensitivities of L-C and C-L cells and 4.1 times the sensitivity of C-C cells.(ABSTRACT TRUNCATED AT 400 WORDS)