Abstract
Diurnal heart rate rhythm was determined continuously by radiotelemetry in the chicken and the rabbit under unrestrained conditions. Clear diurnal heart rate rhythm synchronized with illumination was observed in the chicken, but not in the rabbit. The birds were given single subcutaneous injections of 50 μg of l-thyroxine (T 4)/100 g body weight at 1700 (2 hr before darkness); an increase in heart rate occurred about 2 hr after injection and the effect lasted for 21 hr. Bovine thyrotropin (TSH) at the same dose as T 4 was also injected subcutaneously at 1700. The TSH effect on heart rate started about 3 hr after injection and lasted for 9 hr. The T 4 effect on the rabbit heart rate was compared with that of the chicken. It was first observable at 24 hr after injection and lasted for 19 hr. When T 4 was administered at 0500 (beginning of illumination) in the chicken, the effect appeared 14 hr after injection and lasted for 10 hr (at night). Bilateral vagotomies destroyed the diurnal heart rate rhythm in the chicken. These results indicate that T 4 may modify function of the autonomic nervous system by decreasing vagal tone to the heart in the chicken.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
