L. Stárka

Steroids and intraocular pressure

Abstract The intraocular pressure is dependent upon the aqueous humour formation by the ciliary body and on the outflow through the trabecular meshwork localized in the anterior chamber angle of the eye. In the ciliary body epithelium the active sodium transport has been demonstrated and effects of mineralocorticoids has been suggested but not yet equivocally confirmed. Outflow facility of the trabecular meshwork is connected with the presence of acid mucopolysaccharides. Clinical overdosage of glucocorticoids results in an increase of intraocular pressure, so-called steroid glaucoma. It is explained by the action of glucocorticoids on the stabilization of lysosomal enzymes needed for physiological decomposition of these macromolecular substances. Disbalance of oestrogen supply may lead to disorder in intraocular pressure, too. The occurrence of glucocorticoids, mineralocorticoids, oestrogens and testosterone of endogenous origin in aqueous humour, the metabolism of these hormones and evidence for formation of steroid-receptor complexes is presented.

Corticosterone in the aqueous humour of the rabbit eye.

Corticosterone was identified in the aqueous humour of the rabbit eye by chromatography, acetylation with [14C]acetic anhydride and crystallization to constant specific activity. The level of corticosterone in aqueous humour, determined by a competitive protein binding method, was found to be approximately 10 times lower than the concentration of corticosterone in the peripheral plasma of the female rabbit.

Quantitative determination of endogenous corticosteroids in the rabbit plasma and aqueous humor.

Competetive protein binding technique represents a new very sensitive, specific and rapid method for determination of minute amounts of endogenous steroids. It was used for determination of corticosteroids in the rabbit primary and secondary aqueous humors, as well as in the plasma. Three different sets of aqueous humor samples were analyzed, namely primary aqueous from the left eye, secondary aqueous from the same eye, and primary aqueous from the right eye, both latter withdrawn after an interval of three hours: values of 7.76±4.33, 4.61±2.22, and 4.37±2 73 ng per ml, respectively, were obtained. Plasmatic values, at corresponding time intervals, were nearly ten-times higher, i. e. 5.6+1.65, and 5.9+0.98 μg per 100 ml, respectively. Parallel flurometric determination of plasmatic levels of corticosterone and cortisol was in good agreement, showing 4–5 times prevalence of the corticosterone over cortisol.

Effect of Aldactone Administration into the Rabbit Eye

Potassium canrenoate (Aldactone pro injectione®) was injected into the vitreous of the rabbit eye. Canrenoate was released from the vitreous into the aqueous humour and its concentrations in the anterior chamber were dose dependent and reached a maximum 2–3 h after the injection. The concentrations of sodium ions in the aqueous humour of the treated eye were reduced and those of potassium ions were elevated in comparison with the control eye. Thus the antimineralocorticoid significantly influenced the Na+/K+ ratio.

Cortisol Levels in Human Aqueous Humour and Blood Plasma

Cortisol levels in human aqueous humour and blood plasma were determined by means of the competitive protein-binding method. Cortisol concentration in six patients averaged 80.1 ± 23.8 ng/ml in plasma

Effect of ACTH on the Composition of the Aqueous Humour of the Rabbit Eye

Tetracosactide (Synacthen, Ciba) increases the concentration of corticosterone in the aqueous humour of the rabbit eye. The maximal increase, about 5-fold of the basal level, occurs with a slight delay of approximately 30 min after the maximally stimulated corticosterone level in blood plasma. Glucocorticoid elevation is paralleled by an increase of protein content and a slight rise of glucose in aqueous. A disruption of the blood-aqueous barrier by ACTH similar to the action of alpha-melanocyte-stimulating hormone is suggested.

Effect of Glucocorticoids on the Composition of the Aqueous Humour of the Rabbit Eye

Exogenous corticosteroids (dexamethasone, cortisol) inhibit the adrenal secretion of corticosterone in the rabbit and decrease the concentration of corticosterone in aqueous humour, increase glycaemia and cause a rise in glucose concentration in the aqueous. Except for a slight rise 16 h after the corticosteroid administration no effect on plasma or aqueous content of total protein was observed. This is in striking contrast with the increase of proteins in aqueous humour after ACTH injection. Thus it seems likely that corticosteroids do not mediate the effect of ACTH on the disruption of the blood-aqueous barrier.