Relationship between plasma testosterone and urinary felinine in the growing kitten.

Felinine, a unique amino acid the functions of which are not well understood, is found in large quantities in male cat urine. Our study ran for 13 calendar months and involved taking monthly samples of blood and urine from 10 male and 10 female kittens starting at 6 months of age and measuring urinary felinine and plasma testosterone concentrations. Felinine was detectable at 6 months of age in all cats (range, mean +/- SEM, nmol/mL, 13.8-801.1, 432.3+/-112.2, males and 34.3-393.0, 140.4+/-45.0 females). In entire males, felinine showed a biphasic pattern, peaking (2550 nmol/mL) between 11-13 months of age toward the end of the attainment of puberty then falling to a low (1048 nmol/mL) at 15 months of age then climbing to a peak (3661 nmol/mL) at 17 months of age. Natural plasma testosterone levels in entire males showed a similar biphasic pattern peaking (6.8 pmol/mL) at 12 months of age, falling (1.3 pmol/mL) at 15 months, and finally rising again (12.6 pmol/ml) at 16 months of age. Castration of half the male cats induced a parallel fall in both testosterone and felinine that was reversed following testosterone supplementation. Urinary felinine levels in entire females rose slowly throughout the study and reached 795 nmol/mL at 18 months of age compared to the level of 365 nmol/mL reached by the spayed females: these levels were not significantly different when expressed as felinine/creatinine ratios. We could not detect testosterone in either entire or spayed females and so concluded that felinine was unrelated to testosterone in these groups. There was strong evidence that plasma testosterone levels are positively correlated with urinary felinine levels in male cats. The control of felinine might be sex-linked and may be part of a pheromonal signaling process of the male cat.