iNTRODUCTION

The role of endogenous opioids on the anestrus of domestic animals is well-known (1). The aim of this work was the induction of fertile estrus in queens during seasonal anestrus by the administration of Naloxone (Nx) (antagonist of opioids peptides), calcium (Ca⁺⁺) and GnRH.

MATERIALS AND METHODS

The experiment was carried out on 24 queens of different breeds, age (1-8 y.) and weight (2-5 Kg/b.w.) during the anestrus period (Nov-Dec) for 3 consecutive years (2002-2004). The queens were divided into two groups of 12 subjects each.

Group A

Administration of 0.1 ml/kg/b.w. i.m of Calcium Gluconate 20% (New ICC, Upjohn, Italy) in which 0.4 mg/ml of Naloxone Cloridrate (Diosynth, Holland) was dissolved. The treatment was done for 4 consecutive days for 2 weeks. After the last injection of Ca⁺⁺/Nx, 0.07 mg/kg/b.w. of GnRH-agonist, Buserelin (Suprefact; Hoechst, Italy), as subcutaneous implant, was administered. The GnRH was emulsified with biocompatible silicone grease (Bayer, Italy) in a ratio of 1:6

Group B

Control group, administration of 0.1ml/kg/b.w i.m of physiological solution. Daily behaviour changes and, on alternate days, cytological modifications of vaginal smear (Harris-Schorr staining), were observed in all cats.

RESULTS

The subcutaneous implant of Buserelin was completely reabsorbed in 24 h in all queens of Group A without side effects as well as Ca⁺⁺/Nx injection. The typical proestrus behaviours began 6±1 days after the Buserelin implant, and lasted after 0.7±1.3 days. In proestrus, 11/12 queens (91.6%) were showed a progressive reduction of parabasal cells (<5%) and an increase of superficial cells (>60%). One queen (8.3%) didn't show the typical cytological and behavioural variation of estrus. The estrus lasted 8±1 days with predominance of anucleated superficial cells (40%). Nine heat queens (81.8%) were mated and diagnosed as pregnant, 25 days later by ultrasound evaluation (Sonomed Concept/Mcv S., 5 Mhz, mCX). In the same experimental period, any queen of Group B showed cytological and behavioural signs of estrus

CONCLUSIONS

Estrus induction in cats out of normal reproductive period is important from the biological and clinical point of view. The results showed that, also in the feline species, endogenous opioids exhibit an inhibitory role on the hypothalamus-hypophysis-gonads axis (2-3). The reduction of opioidergic tone by administration of Calcium and Naloxone and the subsequent stimulation by means of the GnRH implant (4-5) induces fertile estrus in seasonal anestrus queens.

REFERENCES

1. Concannon P.W. (1993), J. Reprod. Fertil., Suppl. 47: 3-27.

2. Wang D. et al., (1999), J. Biol. Chem., 274:81-94

3. Aiudi G.et al., (2001), J. Reprod. Fertil., Suppl., 57, 335-337.

4. Sciorsci R.L. et al., (2000), Immunopharmacol.& Immunotoxicol., 22, 575.

5. Walsh J.P. et al., (2001), Neuroendocrinology, 73, 1, 26-36.