A Mechanism for Ovulation Number Control.

Every menstrual cycle, many follicles begin to develop but only a specific number ovulate. This ovulation number determines how many offspring are produced per litter, and differs between species. The physiological mechanism that controls ovulation number is unknown; a class of mathematical models can explain it, but these models have no physiological basis. Here, we suggest a physiological mechanism for ovulation number control, which enables selection of a specific number of follicles out of many, and analyze it in a mathematical model of follicular growth. The mechanism is based on a signal, intra-follicular androgen concentration, that measures follicle size relative to the other follicles. This signal has a biphasic effect, suppressing follicles that are too large or too small compared to others. The ovulation number is determined by the androgen inhibitory thresholds. The model has a scaling symmetry that explains why the dominant follicles grow linearly with time, as observed in human ultrasound data. This approach also explains how chronic hyperandrogenism disrupts ovulation in polycystic ovary syndrome (PCOS), a leading cause of infertility. We propose specific experiments for testing the proposed mechanism.

Occurrence of seizures in association with work-related stress in young male army recruits.

PURPOSE: To examine the risk of undergoing an epileptic seizure as a function of differing levels of occupational stress (physical and mental) in new military recruits with no previous history of epilepsy or with epilepsy in remission for over 2 years. METHODS: The medical records of over 300,000 18-year-old men recruited to the Israeli army between mid-eighties and mid-nineties were used to assemble a cohort, which was followed for a period of 30 months. The severity of epilepsy at recruitment was determined according to four categories, 0 (no history of seizures) and 1-3 (history of seizures with different relapse-free periods, with or without treatment). The soldiers were subdivided according to their occupational categories to: combat units (CU), maintenance units (MU), and administrative units (AU). RESULTS: The annual incidence rates per 100,000 in category 0 were 317, 298, and 401 in AU, MU, and CU, respectively. The incidence of seizures in category 0 was higher (relative risk [RR]= 1.29, CI = 1.03-1.62) in CU compared to AU and MU. No differences were found for seizure recurrence among various occupational groups. CONCLUSION: The increased risk of seizures in CU compared to AU and MU may indicate contribution of service conditions in CU, like physical and mental stress. The equivalent rates of seizure relapse, regardless of the type of occupation, suggests the need for minimal occupational restrictions for epilepsy patients who have been free of seizures for long periods.

Comparison of three methods of pre-employment medical evaluations.

BACKGROUND: Increasing efforts are being made to prevent sickness absence and to increase worker efficiency, including the use of costly pre-employment medical assessment of white-collar workers and labourers, excluding occupations for which medical supervision is required by law. AIM: To investigate whether filling out an occupational health questionnaire (OHQ) as pre-employment assessment was more efficient than previously used protocols which included a physical examination and laboratory tests performed for each applicant. METHODS: Retrospective study comparing three groups of job applicants: Group A--applicants examined by an occupational physician (OP); Group B--applicants examined by a general practitioner (GP) whose medical records were subsequently evaluated by an OP and Group C--the applicant filled out an OHQ which was evaluated by an OP. RESULTS: The study included 1940 pre-employment assessments divided into groups A (618), B (256) and C (1066). The restriction rate was 2.1, 1.2 and 2.3%, respectively. The lowest restriction rate (1.4%) was among applicants 29 years old and younger and the highest one (3.6%) among 50 years and older. The most frequent diagnoses among restricted applicants were musculoskeletal and circulatory diseases (15 and 12%, respectively). CONCLUSIONS: The restriction rate achieved by medical examinations either done by an OP (Group A) or by a GP (Group B) was the same as in OHQ (Group C). The use of a self-administered questionnaire evaluated by an OP is the preferred method of pre-employment evaluation for non-hazardous occupations.