Quantitative evaluation and determination of the biological potency of iontophoretically applied luteinizing hormone-releasing hormone (LRH)

A series of experiments was performed to establish the rate of release for tritium-labelled luteinizing hormone-releasing hormone (LRH) and to establish its biological activity. The in vitro iontophoretic release of labelled LRH from glass micropipettes was determined by liquid scintillation counting. The release of LRH was found to have a non-linear relationship with charge. Much higher charges were needed to iontophorese labelled LRH in detectable quantities as compared to that needed to iontophorese norepinephrine. It is thought that because of the size and solubility of LRH. its release from micropipettes depends on electroosmosis. A 5 nA current was found to be the most effective means of retaining LRH in the glass pipettes. In order to assess the biological activity of the iontophoresed LRH molecule, oestrone-treated, ovaricctomized female rats were given intravenous injections of either 50 ng of LRH, samples of LRH collected from iontophoresis or saline. The injection of LRH or the iontophoresed LRH significantly increased luteinizing hormone levels in these animals, whereas saline administration had no effect. It is suggested that LRH can be reliably iontophoresed from glass micropipettes and that its biological activity is not altered by application of a charge and movement of the molecule through the micropipette orifice.