My blood pressure in the morning is usually around 135/85 systolic and dyastolic but rises to around 145/87 in the afternoon; what could be resposible?

Nervous system?: In the morning, your parasympathetic nervous system (pns) is more active, this will tend to keep your BP low. However as the day progresses you may be overly actviating your sympathetic nervous system (sns)- this could cause an increase in bp. Other things to consider are caffeine, sugar, fried foods and other stressors you may be exposed to during the day.

Hypertension: The upper limit for blood pressure is 140/90. If you are higher than that you should be treated.. Diet, exercise, weight loss, salt restriction, and medications are options.