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N. C. Jackson, H. Jackson, J. H. Shanks, J. S. Dixon, and R. G. Lendon

Summary. Gonadotrophin binding to rat Leydig cells after a single administration of ethylene dimethanesulphonate (EDS) (75mg/kg i.p.) was followed by using intratesticular microdoses of 125I-labelled hCG, whilst corresponding morphological changes in the testicular interstitium were studied with light and electron microscopy. No discernible effect on 125I-labelled hCG binding compared with controls was observed until 24 h after treatment. Between 24 and 32 h a sharp decline in binding occurred which was correlated with extensive Leydig cell destruction. By 48 h the 125I-labelled hCG binding was negligible and no morphologically recognizable Leydig cells were found at this time. The specific binding remained low until 21 days after treatment and then a marked increase occurred to give nearly normal levels by 49 days. This was consistent with a generalized repopulation of the interstitium with Leydig cells, seemingly the result of differentiation of fibroblast-like precursor cells.

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In order to decide whether the rabbit method or the rhesus monkey test is better suited for routine vaginal tolerance tests of spermicidal preparations, combined trials employing both techniques were carried out in the two laboratories in which the tests had been developed.

A `double-blind' experimental design was used in which three unknown, coded compounds were tested jointly in both laboratories and evaluated independently and reciprocally after transatlantic exchange of the resulting histological material. Both test methods and the scoring systems employed in the assessment of findings are described and illustrated by representative photomicrographs.

There was good agreement between both methods for two of the three preparations tested. For the third preparation, the rabbit test results were more consistent with the available clinical data than those of the monkey test.

It was concluded that the rabbit technique is more sensitive than the monkey test. Since it has several obvious practical advantages over the latter, it is proposed that the rabbit vagina test should be generally adopted as the standard method for establishing the local tolerance of new spermicidal preparations for vaginal use.