1 Leptin is a powerful and influential hormone produced by your fat cells. 2  It plays a key role in regulating energy intake and energy expenditure.
(Upgrades are not available on fares in the L, T, and U range, however, which are the most deeply discounted.) To calculate the price of an upgrade, Delta charges a dollar amount per 500 miles. $50: Up to 500 miles. $75: 501-1000 miles. $100: 1001-1500 miles.
P fare is a Y fare with an instant upgrade. Y-UP passengers (A and P fares) are re-accommodated as first class passengers. If F is not available you can sit in coach and get compensated with a Delta travel voucher. Q.