PT  - JOURNAL ARTICLE
AU  - Rodela, Tammy M.
AU  - Wright, Patricia A.
TI  - Metabolic and neuroendocrine effects on diurnal urea excretion in the
mangrove killifish <em>Rivulus marmoratus</em>
AID  - 10.1242/jeb.02289
DP  - 2006 Jul 15
TA  - Journal of Experimental Biology
PG  - 2704--2712
VI  - 209
IP  - 14
4099  - http://jeb.biologists.org/content/209/14/2704.short
4100  - http://jeb.biologists.org/content/209/14/2704.full
SO  - J. Exp. Biol.2006 Jul 15; 209
AB  - In mangrove killifish Rivulus marmoratus, urea excretion (Jurea) follows a distinct diurnal pattern with the highest rates between 12:00 h and 18:00 h. We investigated the regulating mechanisms that underlie temporal rhythms in Jurea in R. marmoratus. We hypothesized that the daily pattern of Jurea in R. marmoratus is (1) due to diurnal changes in urea synthesis rates and ultimately metabolic rate and/or (2) controlled by neuroendocrine messengers. Oxygen consumption and whole body urea content in R. marmoratus demonstrated a clear diurnal pattern with maximum rates for both parameters occurring at 12:00 h. A strong synchrony between diurnal patterns of oxygen consumption, whole body urea content and Jurea implicated metabolic regulation of the diurnal Jurea pattern. Ketanserin, a 5-HT2 receptor antagonist, and RU-486, a cortisol receptor antagonist, were used to test the second hypothesis. Increasing antagonist concentrations of either ketanserin or RU-486 resulted in dose-dependent decreases in Jurea. Application of a single dose of either antagonist significantly decreases Jurea for up to 12 and 6 h for ketanserin and RU-48, respectively. Repeated exposure to doses of either ketanserin or RU-486 did not abolish the diurnal pattern in Jurea; however, there was a significant decrease in the amplitude of the rates. Taken together, these findings indicate that the diurnal pattern of Jurea in R. marmoratus are regulated by both metabolic and neuroendocrine factors. We propose that cortisol and 5-HT influence the absolute rate of urea excretion by altering the permeability of the gill membrane to urea and/or the rate of urea synthesis.