Evidence for suppression of serum LH without elevation in serum estradiol or prolactin with a brain-enhanced redox delivery system for estradiol

Abstract

We developed a redox system for brain-enhanced delivery of estradiol based on an interconvertible dihydropyridine ⇌ pyridinium salt carrier. Estradiol (E2), when combined with the lipoidal carrier, readily crosses the blood-brain barrier. The carrier, when oxidized, reduces the rate of exit of the estradiol-carrier complex from the brain. Subsequent hydrolysis of the carrier provides sustained production of estradiol in the brain. The aim of the study was to evaluate the effects of single vs. multiple injections of the estradiol-chemical delivery system (E2-CDS) on both central and peripheral estrogen-responsive tissues. Ovariectomized Sprague-Dawley rats received an intravenous injection of E2-CDS at 10, 33, 100 or 333 ug/kg BW or the drug vehicle, dimethyl sulfoxide (DMSO; 0.5 ml/kg) every 2 days for 7 injections (2 weeks) or a single injection only at 2 days before sacrifice. With a single injection, E2-CDS did not affect serum luteinizing hormone (LH) levels at the 10 ug/kg dose but caused a dose-dependent reduction in serum LH of 39–52% at the dose range of 33 to 333 ug/kg. By contrast, multiple injections of E2-CDS caused a 32 to 76% reduction in serum LH levels at doses ranging from 10 ug/kg to 333 ug/kg. Additionally, multiple doses of E2-CDS caused a dose-dependent reduction in body weight at the 10 and 33 ug/kg doses with the higher doses causing no further weight reduction. For both single and multiple dosage groups, serum E2 levels remained unchanged after doses of E2-CDS of 10 and 33 ug/kg, then increased to 21 pg/ml for the single dosage group and to 23 pg/ml for the multiple dosage group at the 100 ug/kg dose, and to 59 pg/ml for singly-injected rats and 60 pg/ml for multiply-injected rats at the 333 ug/kg dose. Serum prolactin concentrations were closely correlated with serum E2 levels for both the single and multiple dose groups. These data reveal that a single or multiple doses of E2-CDS can reduce serum LH levels without elevating serum E2 or prolactin concentrations, supporting the concept of brain-enhanced delivery of estradiol with an estradiol chemical delivery system.