The putative and demonstrated miotic effects of prostaglandins in mammals

The foregoing clearly indicates that there are tremendous differences in the responsiveness of the iris sphincters of different mammalian species to the miotic effects of PGs. The iris sphincter of cats and dogs contracts in response to PGF2 alpha, but not in response to other PGs, at concentrations that can be expected to occur under in vivo physiological conditions. In both of these species, PGF2 alpha, but none of the other PGs tested, yielded a dose-dependent full miosis when applied topically to intact eyes. Although in vivo studies are not available on bovine eyes, in vitro studies show that the isolated bovine iris sphincter exhibits a contractile response in the presence of several PGs, but that the threshold concentration for this response is about hundred-fold higher than the concentration of PGF2 alpha required to cause a similar or an even larger effect on feline or canine iris sphincters. Thus, in contrast to the feline iris, the bovine iris shows low sensitivity and low specificity, exhibiting responses to high concentrations of several PGs. In vivo and in vitro studies also are in full agreement that the iris sphincter of several other species, including rabbits and diurnal primates (rhesus and cynomolgus monkeys, baboons, and humans) do not exhibit similar miotic responses to any of the PGs that had been studied so far. It is difficult to summarize all these findings in a truly quantitative manner because the in vitro studies have used different experimental conditions, especially with respect to the inhibitors or precontracting agents used, while in vivo studies have differed with respect to the form of the PG used and in the mode of its administration. These differences, together with the lack in some instances of adequate descriptions of experimental conditions, must be borne in mind in any effort to compare the effects of PGs on the iris sphincter of different species. Nevertheless, because of the importance of obtaining at least a semi-quantitative picture of the extent of these species differences, the data derived from reports on in vivo studies of miosis have been tabulated in the chapter dealing with the effects of PGs on IOP (see Bito et al., 1989). Results extracted from some of the in vitro studies that have been reviewed in the previous sections are summarized in Table 1. The readers are urged to study the original publications and to bear in mind the problems described in the preceding sections that are encountered when trying to interpret the results presented by van Alphen et al. (1977).(ABSTRACT TRUNCATED AT 400 WORDS)