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The effects of selective D2-dopaminergic receptor stimulation with LY163502 on male rat copulatory behavior were evaluated. LY163502 (25 ng/kg to 25 micrograms/kg s.c.) produced increases in the percentage of sexually inactive rats displaying mounting behavior and ejaculating during the test period. Within this same dose range, LY163502 administration induced an increase in the percentage of non-ejaculator rats that were capable of ejaculation. These findings are viewed as evidence that LY163502 can initiate sexual behavior and lower the threshold for ejaculation. The effects of LY163502 were further evaluated in rats that were capable of ejaculation during the test period. LY163502 (25 ng/kg to 25 micrograms/kg s.c. or p.o.) induced significant reductions in ejaculatory latency. These effects were blocked by prior treatment with centrally active dopaminergic antagonists, RO 22-1319 and sulpiride, but not with a peripherally active antagonist, domperidone. LY163502 administration was also found to inhibit sexual behavior in low doses of 25 pg/kg-10 ng/kg s.c. and in a much larger dose of 25 mg/kg s.c. These inhibitory effects are viewed as behavioral manifestations of selective dopaminergic autoreceptor activation with low doses and as the disruption of sexual behavior by induction of intense stereotypic behavior with high doses.

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We assessed the effects of age and endurance exercise training (treadmill running at 75% maximal running capacity, 1 h/day, 5 days/wk for 10 wk) on the total concentration of insulin-regulatable glucose transporters (GLUT-4) and GLUT-4 mRNA levels in the myocardium of male Fischer 344 rats aged 7, 15, and 25 mo. Myocardial GLUT-4 concentration was quantified with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting and detected with a polyclonal antibody to the GLUT-4 transporter. Myocardial GLUT-4 mRNA levels were quantified with slot-blot analysis and a cDNA probe for GLUT-4. Myocardial GLUT-4 concentration in the 25-mo group decreased 27 and 20% compared with the 7- and 15-mo group, respectively (P < 0.0001 and P < 0.003). GLUT-4 mRNA also decreased significantly in the 25-mo group compared with the 7-mo group (20% in the trained and 11% in the untrained group, P < 0.05). Endurance training did not significantly affect myocardial GLUT-4 concentrations in any age group despite a significant increase in GLUT-4 mRNA in the 7- and 25-mo trained groups. In conclusion, myocardial GLUT-4 protein levels in the rat are significantly decreased with age but are unaffected by 10 wk of treadmill running.