PHYSIOLOGICAL AND NEUROENDOCRINE CORRELATES OF SOCIAL POSITION IN NORMOTENSIVE AND HYPERTENSIVE RAT COLONIES

The hypothesis to be tested was that socially dominant (D) males in a mixed gender rat colony will have: higher blood pressure (BP) decrease d hypothalamic pituitary axis (HPA) activity measured by plasma cortic osterone (C) and increased sympathetic activity measured by plasma nor adrenaline (NA) as compared to socially subordinate (S) males. BP was measured continuously by implanted aortic telemetry (Data Sciences, MN ), plasma noradrenaline measured by HPLC with electrochemical detectio n and plasma C by RIA. Colonies were established using 8 of each sex o f 4 strains: SHR, WKY, and our two Y chromosome congenic strains, SHR/ y and SHR/a. Social ranking was determined by physical scarring scores , overall locomotor activity and patrol behaviour. D males had higher BP (active dark cycle) across strains compared to subordinates S: SHR - 180 vs 148 mmHg, WKY - 145 vs 142 mmHg, SHR/y - 185 vs 145 mmHg, SHR /a - 180 vs 160 mmHg. Using an acute stressor, BP responsiveness was h igher in D than in S SHR and SHR/y males. D males had higher NA levels than S males across strains: (SHR-76% increase, WKY-31% increase, SHR /y-29% increase, SHR/a-40% increase). S males had significantly higher C levels than D males across strains (SHR-29% increase, WKY-123% incr ease, SHR/y-25% increase, SHR/a-61% increase). The hypertensive Y chro mosome (SHR or SHR/y) produced higher SEP during the active dark cycle in D males than in D males with a normotensive Y chromosome (WKY or S HR/a). In conclusion, D males from related hypertensive strains showed elevated sympathetic activity measured by plasma NA and reduced HPA a ctivity measured by plasma C as compared to S males.