A pharmaceutical composition, preferably ophthalmic solution or ophthalmic suspension, useful for treating animals of the mammalian species, including humans, to reduce or maintain intraocular pressure in the eye contains as its pharmacologically active ingredient one or more compounds of the formula ##STR1## where X is O, S or NH; n is an integer with the values of 0, 1 or 2; when n is 0 then R.sub.1 is lower alkyl having 1 to 6 carbon atoms and R.sub.2 is H or lower alkyl having 1 to 6 carbon atoms; when n is 1 or 2, then R.sub.1 and R.sub.2 are methylene (CH.sub.2), or methylene substituted with an R.sub.5 group where R.sub.5 is lower alkyl of 1 to 6 carbons; R.sub.3 and R.sub.4 independently are H or lower alkyl having 1 to 6 carbons; R.sub.6 is H or lower alkyl of 1 to 6 carbons.

Compounds of the formula ##STR1## where X is O or S; R.sub.1 is lower alkyl having 1 to 6 carbons; R.sub.2 is H, lower alkyl having 1 to 6 carbons; or OR.sub.2.sup.* where R.sub.2.sup.* is lower alkyl having 1 to 6 carbons; Y is O, S or NH; and R.sub.3 is H, lower alkyl having 1 to six carbons, or C(O)R.sub.3.sup.* where R.sub.3.sup.* is lower alkyl having 1 to 5 carbons, with the proviso that the YR.sub.3 group is not disposed in the ortho position on the benzene nucleus relative to the 2-amino group of the oxazoline or thiazoline heterocycle, are active in maintaining or reducing intraocular pressure in the mammalian eye, and are active as vasoconstrictors and capable of reducing or controlling intraocular bleeding of the mammalian eye.

A compound of formula I in which: ring A is one of the five alternative multi-cyclic rings as shown wherein a dotted line adjacent to a bond indicates that a single bond or a double bond may be present at that position; X is nitrogen, oxygen or sulfur; R is hydrogen, lower straight or branched chain alkyl of 1 to 6 carbon atoms, or lower straight or branched chain alkenyl of 2 to 6 carbon atoms, a cycloaliphatic ring of 3 to 6 carbon atoms, phenyl optionally mono- or di-substituted with hydroxy, halogen, alkyl of 1 to 3 carbon atoms or alkoxy of 1 to 2 carbon atoms, or methylenedioxyphenyl; or a stereoisomer, or a pharmaceutically acceptable salt thereof. These compounds have .alpha..sub.2 receptor blocking activity and hence find use in the treatment or palliation of elevated intraocular pressure, non insulin-dependent diabetes, male impotence and obesity.

Methods and pharmaceutical formulations of alpha.sub.2 agonists and alpha.sub.3 antagonists which are useful in lowering intraocular pressure (IOP) and treatment of intraocular hypertension. Co-administration of a therapeutic amount of alpha.sub.2 agonist with a potentiating amount of alpha.sub.3 agonist is effective in lowering IOP and treatment of intraocular hypertension.

A compound of formula I ##STR1## in which: ring A is one of the five alternative multi-cyclic rings as shown wherein a dotted line adjacent to a bond indicates that a single bond or a double bond may be present at that position; X is nitrogen, oxygen or sulfur; R is hydrogen, lower straight or branched chain alkyl of 1 to 6 carbon atoms, or lower straight or branched chain alkenyl of 2 to 6 carbon atoms, a cycloaliphatic ring of 3 to 6 carbon atoms, phenyl optionally mono- or di-substituted with hydroxy, halogen, alkyl of 1 to 3 carbon atoms or alkoxy of 1 to 2 carbon atoms, or methylenedioxyphenyl; or a stereoisomer, or a pharmaceutically acceptable salt thereof. These compounds have .alpha..sub.2 receptor blocking activity and hence find use in the treatment or palliation of elevated intraocular pressure, non insulin-dependent diabetes, male impotence and obesity.