Emesis in monkeys following exposure to ionizing radiation

Area of Science:

• Radiation biology
• Primate research
• Toxicology

Background:

• The emetic response to radiation is a critical factor in assessing radiation sickness.
• Understanding dose-response relationships is vital for predicting and mitigating radiation effects.

Purpose of the Study:

• To investigate the incidence and pattern of vomiting in rhesus monkeys following exposure to prompt radiation.
• To characterize the dose-response relationship of radiation-induced emesis in a primate model.

Main Methods:

• 129 male rhesus monkeys were exposed to neutron/gamma radiation (0.4 ratio, 50 ms pulse width) at doses from 700 to 5600 rad (midhead).
• Animals were fasted 18 hours pre-exposure and monitored for vomiting incidence and timing for 2 hours post-exposure.

Main Results:

• Vomiting incidence increased with radiation dose up to 1000 rads.
• Above 1000 rads, vomiting incidence decreased as the radiation dose increased.
• The pattern of total vomits per dose group mirrored the incidence of emesis, with most episodes occurring 20-50 minutes post-irradiation.

Conclusions:

• The dose-response curve for radiation-induced emesis in rhesus monkeys is non-linear, with a peak incidence around 1000 rads.
• These findings highlight a complex biological response to radiation, where higher doses may paradoxically lead to a lower observed emetic response.
• The timing of emetic episodes provides insights into the physiological mechanisms of radiation sickness in primates.