Single melatonin injection enhances the testicular artery hemodynamic, reproductive hormones, and semen parameters in German shepherd dogs

This study aimed to determine the effects of melatonin administration on testicular vascular perfusion in relation to steroid hormones and semen characteristics in dogs. The study included 12 normospermic German shepherd dogs (weighed 35 ± 0.5 kg and aged 4 ± 0.5 years). Males received a single melatonin administration (melatonin dimethyl sulfoxide + corn oil via subcutaneous route; MEL; n = 6), while the rest of the animals served as controls (dimethyl sulfoxide + corn oil; Control; n = 6). Males were subjected to routine examination on days -15, 0, 15, 30, 45, and 60. All examined dogs were subjected to Doppler screening, semen collection, and blood sampling. The MEL group showed a significant (P < 0.05) elevation in semen volume, concentration, percentage of sperm motility, and total sperm × 10(6) / ejaculate compared to other control males. Doppler indices as resistance (RI) and pulsatility (PI) indices declined (P < 0.05) from D 30 (1.02 ± 0.01) until day 60 (0.87 ± 0.02) of treatment. In MEL males, the peak systolic point of velocity (PSV; cm/sec) of the testicular artery elevated (P < 0.05) on day 60 (20.15 ± 0.99) compared to its value on day 0 (17.39 ± 1.84). On D 60, the levels of testosterone (T), estradiol 17-ß (E2), and nitric oxide (NO) elevated (P < 0.05). A negative correlation was detected between testicular volume, scrotal circumference (SC), T levels, Doppler indices, and velocities. In conclusion, single melatonin administration could improve testicular vascularization via increasing Doppler velocities and intratesticular colored areas. In addition, it could improve semen picture and steroids (T and E2) and nitric oxide. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-022-03487-y.