AGE DOES NOT AFFECT CONTRACTILE RESPONSES OF THE ISOLATED RHESUS-MONKEY CILIARY MUSCLE TO MUSCARINIC AGONISTS

In primates, ciliary muscle contraction causes accommodation and facil itates aqueous outflow. In living rhesus monkeys, accommodative, outfl ow facility, and ciliary muscle movement responses to cholinergic agon ists all decline with age. We developed an apparatus to determine in v itro whether the latter is related to intra- or extra-ciliary muscle f actors, and whether ciliary muscle contraction in the coronal (putativ ely more accommodation-relevant) and longitudinal (putatively more fac ility-relevant) vectors can be dissociated pharmacologically. In fresh ciliary muscle strips, carbachol and aceclidine each induced dose-dep endent contraction in the longitudinal and coronal vectors. With neith er drug was there any apparent dissociation of the responses in the tw o vectors. Atropine pretreatment completely prevented a supramaximal d ose of carbachol from inducing ciliary muscle contraction in either ve ctor. Ciliary muscle strips responded to several cholinergic agonists as well on day 2 (24-32 hours post-enucleation) as on day 1 (1-9 hours post-enucleation) when kept in a cell culture medium at 4-degrees-C. By light microscopy, the general architecture of the ciliary muscle, t he muscle bundles, and the single muscle cells appeared normal; howeve r, cellular and nuclear swelling were apparent following the 32-hour c ulturing period. Contractile responses to near-maximal doses of carbac hol and aceclidine did not vary markedly with age in either vector, su ggesting that the age-related decrease in ciliary muscle mobility in v ivo is due to extra-muscular restrictive factors rather than diminishe d muscular contractility.