Effects of administration of testosterone, dihydrotestosterone, oestrogen and fadrozole, an aromatase inhibitor, on sex skin colour in intact male rhesus macaques

Abstract

For defining the mechanism of control of sex skin colour in male rhesus macaques (Macaca mulatta) by hormones, a spectrocolorimeter was used to monitor skin redness after administration of testosterone, dihydrotestosterone (a non-aromatizable androgen), oestradiol or fadrozole (an aromatase inhibitor that blocks the conversion of testosterone to oestrogen). Skin blood flow was measured by laser doppler. Eight 9-14 kg, 5-9 year old intact male rhesus macaques were given hormone, fadrozole or vehicle treatments in a cross-over experimental design. Baseline blood flow and colour measurements were taken in four paired tattoo defined areas on the back and legs of each animal (one pair in non-sex skin, three pairs in sex skin). Colour and blood flow measurements were taken 3-4 days after the first dose and, thereafter, once a week for 3-6 weeks. Measurements taken after treatments were compared with baseline and intra-animal comparisons were made between treatment and vehicle for each animal. In all animals after administration of 4 mg testosterone kg-1 (long-acting), redness in the sex skin areas increased (P = 0.032) by day 3 and returned to baseline values by day 7. Administration of 1 mg oestradiol kg-1 day-1 for 4 days caused increased redness in all animals (P = 0.007) similar in magnitude to that caused by testosterone. Administration of 0.1 mg dihydrotestosterone kg-1 day-1 for 4 days resulted in a nonsignificant decrease in redness (P = 0.09) on days 3-7. Treatment with fadrozole (0.25-0.5 mg kg-1 day-1) for 3 weeks caused sex skin to become significantly less red during treatment (P = 0.014). There was no significant change in redness in non-sex skin areas during any treatment. Sex skin blood flow increased in animals treated with testosterone, correlating with increased redness (R = 0.906), while blood flow in non-sex skin was unchanged. Increased redness after treatment with testosterone and oestrogen, no change in redness with treatment with dihydrotestosterone and a decrease in redness after treatment with fadrozole support the conclusion that oestrogen controls sex skin redness, and testosterone acts indirectly through conversion to oestrogen to cause increased sex skin redness in male rhesus macaques.

Color in competition contexts in non-human animals

“…Bright skin colour in primates is pink/red, blue, or a combination of the two; colours which are easy to produce, in evolutionary terms (Grubb, 1973). Pink/red is thought to be due to the colour of oxygenated haemoglobin in highly-vascularised, blood-filled tissues (Rhodes et al, 1997). In contrast, blue is a structural colour, due to the physical interactions of light waves with biological structures.…”

“…The degree of coloration is highly variable among individuals (Rhodes et al, 1997;Waitt, Gerald, 13 Little, & Kraiselburd, 2006), ranging from light pink to dark red, with more variation in genital colour than on the face or rump (Higham, Pfefferle, Heistermann, Maestripieri, & Stevens, 2013). Castration causes a decline in skin colour, although it does not reach normal body skin colour, possibly due to adrenal androgens (Vandenburgh, 1965).…”

“…Castration causes a decline in skin colour, although it does not reach normal body skin colour, possibly due to adrenal androgens (Vandenburgh, 1965). Experimental administration of both testosterone and oestrogen also increases reddening of the skin in these areas, but not of other areas (Vandenburgh, 1965), as a result of increased epidermal blood flow (Rhodes et al, 1997). Treatment with an aromatase inhibitor (fadrozole) reduces red colour, suggesting that the change in red results from the aromatization of testosterone to oestrogen (Rhodes et al, 1997).…”

Effect of Pueraria mirifica on the Sexual Skin Coloration of Aged Menopausal Cynomolgus Monkeys

“…The influence of estrogen on the sexual skin area around the perineum to the base of the tail has been reported for the nonhuman old world primates [11,12]. The color of the skin of rhesus monkeys (Macaca mulatta) has been shown to be correlated with high concentrations of estrogen before ovulation, whereas the skin shows its palest coloration at menstruation [13,14].…”

“…In addition, the sexual skin of cynomolgus monkeys (Macaca fascicularis) [15], pig-tailed macaques (Macaca n e m e s t r i n a ) [ 1 6 ] , a n d m a n g a b e y m o n k e y s (Cercocebus atys lunulatus) [11] display maximal edema and swelling associated with estrogen f l u c t u a t i o n d u r i n g t h e m e n s t r u a l c y c l e . Administration of estrogen caused increasing redness of the sexual skin area of ovariectomized rhesus monkeys [13,16] and intact male rhesus monkeys [12]. The sexual skin is thus considered to be an external indicator of estrogenic effect in monkeys.…”