The effect of elevated progesterone levels on intraocular pressure in lions (Panthera leo)

Recently, we reported that intraocular pressure (rop) in juvenile male lion s (Panthera lee) is significantly higher than in juvenile lionesses. Whilst we could not ascertain the basis for this gender-related difference, we su spected that they were the result of fluctuations in levels of sex hormones . Because 19 of the 22 lions described in our previous report had to be re- anaesthetized, we repeated tonometry in these animals, to try and correlate between Iop and the levels of progesterone, oestrogen and/or testosterone. Based on elevated (>5 ng ml(-1)) levels of progesterone, lionesses were di vided into a luteal (n = 8) and a non-luteal (n = 13) group. In the luteal group, mean Iop was 27.07+/-2.15 mm Hg, significantly (P = 0.001) higher th an in the non-luteal group (21.61+/-2.70 mm Hg). Oestrogen, testosterone, a nesthesia and age had no significant effect on rep. It is suggested that el evated progesterone levels associated with the luteal phase in lionesses ca use increased resistance to aqueous humor outflow, leading to IOP elevation . Similar ocular hypertension has been observed in rabbits following exogen ous progesterone application, but this is the first report on the hypertens ive effect of endogenous progesterone on IOP. (C) 1999 Harcourt Publishers Limited.