The positive effect of testosterone replacement therapy on psychosocial well-being in hypogonadal men has been demonstrated by various psychometric tests. However, there is no report available that objectively demonstrates the effect of testosterone on the function of the central nervous system in men. In this report we studied cerebral perfusion in seven hypogonadal men on testosterone replacement therapy. The blood perfusion to the central nervous system was assessed using single-photon emission-computed tomography. (99 m)Tc-hexamethyl-propylene-amine oxime crosses the blood brain barrier and localizes in brain tissue, depending on the intensity of the local blood flow. Psychosocial well-being was assessed with an Androgen Deficiency in Aging Men questionnaire. The study demonstrated that testosterone replacement enhanced cerebral perfusion in midbrain and superior frontal gyrus (Brodman area 8) at 3-5 wk of treatment. At 12-14 wk the study continued to show increased perfusion in midbrain in addition to the appearance of a new activated region in the midcingulate gyrus (Brodman area 24). The results of this study provide objective evidence that testosterone and /or its metabolites increased cerebral perfusion in addition to the improvement in cognitive function.

Splanchnic and splenic erythrocyte volumes decrease during postural changes and exercise to help maintain central blood volume and cardiac output. The contribution of this compensatory mechanism to hemodynamic stability during dialysis has not been studied, however. In 8 ESRD patients, age 51.0 +/- 4.5 years old, we measured changes in the splanchnic/splenic erythrocyte volume during dialysis by tagging the patients' erythrocytes with technetium and following abdominal radioactivity over time. Splanchnic radioactivity decreased to 90.2 +/- 3.8% (mean +/- SEM) of the baseline value after 2 hr of accelerated fluid removal (3.7 +/- 0.4 liters) during dialysis (DUF), while it remained relatively unchanged after two hours of dialysis without fluid removal (DD) [106.5 +/- 2.3%, P (DUF vs. DD) = 0.03]. Splenic radioactivity decreased to 89.2 +/- 5.0% of the initial value during DUF versus 103 +/- 3.8% during DD, but the decrease was noted only during the last 30 minutes of DUF and did not attain statistical significance. Autonomic nervous system integrity was measured by the spontaneous variation of the R-R interval during deep respiration (E/I ratio) and by the Valsalva ratio. The mean E/I and Valsalva ratios in the eight patients were 1.13 +/- 0.03 (+/-SEM) and 1.42 +/- 0.1 respectively, suggesting reasonably adequate autonomic nervous system functioning. The results suggest that contraction of the splanchnic, and possibly the splenic, vascular beds occurs during fluid removal associated with hemodialysis. The resultant addition of erythrocytes to the circulation may help maintain central blood volume and cardiac output.