Chronic ethanol intake inhibits both the vasoactive intestinal peptide binding and the associated cyclic AMP production in rat enterocytes

Vasoactive intestinal peptide mRNA and immunoreactivity are decreased in fetal alcohol syndrome model

Vasoactive intestinal peptide (VIP) regulates growth in the early post-implantation embryo. Previous work has demonstrated that peptide agonists (SALLRSIPA and NAPVSIPQ) from downstream mediators that are regulated by VIP were able to prevent the alcohol-induced fetal death, growth restriction and microcephaly associated with fetal alcohol syndrome. Here we evaluated the role of VIP in this mouse model of fetal alcohol syndrome, to determine if fetal or maternal levels of VIP are altered. In addition, we evaluated whether peptide treatment would alter the effects of alcohol on VIP levels. Treatment groups included control, alcohol, and alcohol+peptides. VIP levels were measured with enzyme immunoassay [EIA] (Peninsula Laboratories, Belmont, CA). Quantitation of VIP expression was measured with rt-PCR using mimic cDNA primers. Embryo/decidual VIP levels were similar in control and alcohol-treated groups 6 h after treatment. However, in the embryo/deciduas at 12 and 24 h, VIP levels were below the EIA's detection limit in the alcohol-treated groups, and significantly lower than the control or peptide-pretreated groups (p<0.05). Maternal cortex VIP levels were undetectable and significantly lower in the alcohol-treated group than control or peptide+alcohol group at 6 and 12 h (p<0.001). VIP mRNA expression was quantitated in the embryo and deciduas, with a significant decline noted at 6 h to 58% of control levels (p=0.02). Pretreatment with the peptides attenuated the alcohol-induced decrease in VIP mRNA. These studies demonstrate that treatment with alcohol can decrease the expression and immunoreactivity of VIP in both maternal and fetal tissues. This alcohol-induced loss of a recognized regulator of embryonic growth and differentiation may contribute to the sequelae of toxicity observed in fetal alcohol syndrome.

G-protein regulation of adenylate cyclase activity in rat prostatic membranes after chronic ethanol ingestion

BACKGROUND

The possibility that long-term ethanol ingestion might alter either vasoactive intestinal peptide (VIP) content, VIP binding to membrane receptors, G-protein levels or adenylate cyclase activity in rat prostate was tested, as ethanol produces serious alterations in the hypothalamic-pituitary-gonadal axis and several modifications on different elements on signal transduction pathways in other systems.

METHODS

Prostatic membranes from control and ethanol-treated (for 4 weeks) rats were used to study adenylate cyclase stimulation as well as for the immunodetection of stimulatory (alpha(s)) and inhibitory (alpha(i)1-2) G-protein subunits. Studies on VIP binding and cross-linking to receptors were performed using [125I]VIP. Prostatic VIP content was estimated by radioimmunoassay. GTPase activity was quantified by measuring the amount of 32Pi released from [gamma-32P]GTP.

RESULTS

Chronic ethanol ingestion resulted in an increased presence of VIP in the rat prostate without any change on the VIP receptor/effector system in this gland. By contrast, the basal adenylate cyclase activity as well as the dose-dependent stimulation of this enzyme by either the nonhydrolyzable GTP analogue Gpp(NH)p or the beta-adrenergic agonist isoproterenol were enhanced in prostatic membranes after ethanol intake. Moreover, an increase in the content of G-protein subunits (alpha(S) and alpha(i)1-2) was observed without any change in GTPase activity in this condition. These modifications were accompanied by a significant decrease in rat prostate weight and, consequently, the height of the secretory epithelium in this gland.

CONCLUSIONS

Considering the role of VIP in the mechanisms of secretion and cell proliferation in the prostate, the observed increases in the prostatic content of VIP and G-protein subunits make conceivable that VIP and cAMP signal transduction could be involved in the atrophy of the rat prostate and in the alterations in the composition of seminal fluid that appear in the alcoholic syndrome.

Effect of fetal alcohol exposure on postnatal pituitary adenosine 3', 5'-cyclic phosphate content and growth hormone release

This study examines the influence of fetal ethanol (ETOH) exposure and pair-feeding dams on postnatal, releasing factor-induced pituitary growth hormone (GH) release and adenosine 3',5'-cyclic phosphate (cAMP) accumulation. Fetuses were exposed to ETOH in utero by feeding dams a 36% (calories derived from ETOH: 6.6% v/v) ETOH liquid diet. Postnatal body weights were measured at sacrifice to evaluate the influence of ETOH on growth. Pituitary weight and protein content were measured to determine if changes in GH secretion or cAMP are proportional to the overall effect of ETOH on the pituitary. Pituitaries from 1-, 10-, and 60-day-old pups were explanted and incubated without hormones or with either somatostatin [somatotropin-release inhibiting factor (SRIF); 10(-9) M], or GH-releasing factor (GRF; 5 x 10(-9) M). Radioimmunoassays were used to determine tissue cAMP content, after extraction, and media GH concentration. Results indicate that fetal ETOH exposure specifically reduces the weight of both male and female pups. However, by 60 days of age, this reduction is not different from that found in pups of pair-fed controls, and both groups weighed less than pups of ad libitum controls. Furthermore, both pituitary weight and protein content were proportionately reduced in ETOH-exposed pups. In regard to releasing factor sensitivity, compared with pituitaries from ad libitum controls, the capacity of GRF to simulate GH release was diminished in 10-day-old males (p < 0.006) exposed to ETOH. On the other hand, the capacity of GRF to stimulate cAMP accumulation was generally enhanced by prenatal ETOH exposure. The capacity of SRIF to depress GH release was diminished in ETOH pups, compared with both pair-fed and ad libitum-fed controls (p < 0.0001). This difference in GH release was more apparent in pituitaries from females than males (p < 0.001). However, the depressed SRIF response was not associated with altered cAMP accumulation. These data suggest that fetal ETOH exposure has a sexually dimorphic effect on pituitary sensitivity to GH-releasing factors that may be related to altered regulation of GH release and susceptibility to growth retardation.

Effect of chronic ethanol administration on the rat pineal N-acetyltransferase and thyroxine type II 5'-deiodinase activities

Chronic ethanol intake resulted in a significant decrease in the rate of ponderal growth and an impaired nyctohemeral profile of pineal N-acetyltransferase (NAT) activity. In ethanol-treated animals, the onset of the nocturnal NAT increase is delayed by 2 hours when compared to control animals. Moreover, pineal NAT nocturnal peak was reached at 4 h (2 hours later than controls), while pineal type II thyroxine 5'-deiodinase (5'-D) nyctohemeral profile was not modified by ethanol administration. The effect of ethanol administration (12 weeks) on 5'-D activity in different tissues was also studied. Ethanol induced a 5'-D activity increase in hypothesis and brain frontal cortex, when compared to control animals. No change in 5'-D activity is observed in either pineal gland, Harderian gland, or brown adipose tissue. Since basal values of 5'-D activity in hypophysis or brain frontal cortex are particularly dependent on serum thyroxine (T4) concentration, the effect of chronic ethanol administration on thyroid hormone levels was studied. Serum T4 levels in ethanol-treated animals were significantly decreased when compared to controls at any time point studied. However, no change in serum 3',3,5-triiodothyronine (T3) levels were found.