THE SPONTANEOUSLY HYPERTENSIVE RAT Y-CHROMOSOME PRODUCES AN EARLY TESTOSTERONE RISE IN NORMOTENSIVE RATS

Objective: To investigate the relationship between testosterone and bl ood pressure during the rapid development phase of blood pressure rise in four strains of rats: Wistar-Kyoto (WKY) rats; spontaneously hyper tensive rats (SHR); SHR/y, a substrain with an SHR Y chromosome and WK Y rat autosomes and X chromosomes; and SHR/a, a substrain with SHR aut osomes and X chromosomes and the WKY rat Y chromosome. Methods: Blood pressure was measured every 2 weeks by the tail-cuff method, and was v erified in selected rats at 23 weeks by aortic telemetry. Serum testos terone was measured, by radioimmunoassay, every 2 weeks from 5 to 23 w eeks of age. Results: During the rapid phase of blood pressure rise, b etween 5 and 9 weeks of age, there was a significantly larger rise in serum testosterone in SHR and SHR/y than in WKY rats and SHR/a groups. The hypertensive Y chromosome in the SHR and SHR/y accelerated peak t estosterone approximately 4 weeks earlier, and blood pressure was incr eased in these two groups compared with the SHR/a and WKY rat groups, respectively. A gene on the SHR Y chromosome (Tty) affecting the timin g of testosterone in development is proposed. At approximately 15 week s of age testosterone levels decreased sharply towards prepubertal lev els in WKY rats and at 23 weeks in SHR/y whereas testosterone levels w ere maintained in SHR and SHR/a, which suggests an autosomal component . Conclusion: The SHR Y chromosome may accelerate the start of puberty and a cascade of molecular and neuroendocrine events that raise blood pressure.