IN OVO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN EXPOSURE IN 3 AVIAN SPECIES .2. EFFECTS ON ESTROGEN-RECEPTOR AND PLASMA SEX STEROID-HORMONES DURING THE PERINATAL-PERIOD

As opposed to mammals, the heterogametic sex in birds is female, and s exual differentiation of the central nervous system away from the intr insic male pattern is dependent on ovarian estrogen secretions during the perinatal period, The contamination of aquatic systems with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds has been su ggested to be responsible for decreased reproductive success in certai n wild fish-eating bird populations. Since TCDD has been shown to alte r estrogenic status in laboratory animals, we determined the effects o f in ovo TCDD exposure on hepatic estrogen receptor (ER) concentration s and affinities, and plasma estradiol concentrations during the perin atal period in the domestic chicken (Gallas gallus), domestic pigeon ( Columba livia), and great blue heron (Ardea herodias). Plasma testoste rone levels were also determined in herons as an indication of androge nic status, [H-3]TCDD was injected into the air cell of chicken eggs o n Embryonic Day 4.5 (0.1 mu g/kg egg), pigeon eggs on Embryonic Day 3. 5 (1 mu g/kg egg) and Embryonic Day 14 (3 mu g/kg egg), and heron eggs at approximately Embryonic Day 13 (2 mu g/kg egg). Chickens were euth anized on Embryonic Days 17 and 19, hatch, and Days 2 and 4 after hatc h. Pigeons and herons were either euthanized at hatch or fed an uncont aminated diet for 7 days prior to termination, Between 5 and 10% of th e injected [H-3]TCDD dose was measured in the liver of hatchlings. The re was no effect of in ovo TCDD exposure on hepatic ER levels or plasm a estradiol concentrations in female chickens and pigeons exposed earl y in incubation, In female pigeons exposed during the latter third par t of incubation to a TCDD dose that would cause high embryo lethality if injected early in incubation, hepatic ER concentrations were elevat ed (p < 0.001) and plasma estradiol concentrations were decreased (p < 0.01) at hatch. There was no effect of TCDD exposure on plasma estrad iol levels in male pigeons. In herons, TCDD exposure had no effect on hepatic ER levels or plasma estradiol and testosterone concentrations at either time paint. We conclude that in chicken, pigeon, and great b lue heron hatchlings exposed early in incubation to low doses of TCDD, hepatic ER levels and plasma estradiol concentrations are not biomark ers of toxicity. (C) 1996 Academic Press, Inc.